diff --git a/binaries/data/mods/public/gui/session/menu.js b/binaries/data/mods/public/gui/session/menu.js
index 44b004b929..5562ae2b69 100644
--- a/binaries/data/mods/public/gui/session/menu.js
+++ b/binaries/data/mods/public/gui/session/menu.js
@@ -755,6 +755,7 @@ function toggleDeveloperOverlay()
 
 function closeOpenDialogs()
 {
+	 // TODO: also close message boxes
 	closeMenu();
 	closeChat();
 	closeDiplomacy();
diff --git a/binaries/data/mods/public/gui/session/messages.js b/binaries/data/mods/public/gui/session/messages.js
index ab895deaec..5392657cbf 100644
--- a/binaries/data/mods/public/gui/session/messages.js
+++ b/binaries/data/mods/public/gui/session/messages.js
@@ -101,6 +101,7 @@ var g_FormatChatMessage = {
 	"clientlist": msg => getUsernameList(),
 	"message": msg => formatChatCommand(msg),
 	"defeat": msg => formatDefeatMessage(msg),
+	"won": msg => formatWinMessage(msg),
 	"diplomacy": msg => formatDiplomacyMessage(msg),
 	"tribute": msg => formatTributeMessage(msg),
 	"attack": msg => formatAttackMessage(msg)
@@ -194,6 +195,8 @@ var g_DiplomacyMessages = {
 
 /**
  * Defines how the GUI reacts to notifications that are sent by the simulation.
+ * Don't open new pages (message boxes) here! Otherwise further notifications
+ * handled in the same turn can't access the GUI objects anymore.
  */
 var g_NotificationsTypes =
 {
@@ -246,9 +249,16 @@ var g_NotificationsTypes =
 			"player": player,
 			"resign": !!notification.resign
 		});
-
-		updateDiplomacy();
-		updateChatAddressees();
+		playerFinished(player, false);
+	},
+	"won": function(notification, player)
+	{
+		addChatMessage({
+			"type": "won",
+			"guid": findGuidForPlayerID(player),
+			"player": player
+		});
+		playerFinished(player, true);
 	},
 	"diplomacy": function(notification, player)
 	{
@@ -417,8 +427,7 @@ function findGuidForPlayerID(playerID)
  */
 function handleNotifications()
 {
-	let notifications = Engine.GuiInterfaceCall("GetNotifications");
-	for (let notification of notifications)
+	for (let notification of Engine.GuiInterfaceCall("GetNotifications"))
 	{
 		if (!notification.players || !notification.type || !g_NotificationsTypes[notification.type])
 		{
@@ -745,6 +754,13 @@ function formatDefeatMessage(msg)
 	);
 }
 
+function formatWinMessage(msg)
+{
+	return sprintf(translate("%(player)s has won."), {
+		"player": colorizePlayernameByID(msg.player)
+	});
+}
+
 function formatDiplomacyMessage(msg)
 {
 	let messageType;
diff --git a/binaries/data/mods/public/gui/session/session.js b/binaries/data/mods/public/gui/session/session.js
index a92b01e000..4f5f441216 100644
--- a/binaries/data/mods/public/gui/session/session.js
+++ b/binaries/data/mods/public/gui/session/session.js
@@ -37,6 +37,11 @@ var g_IsObserver = false;
  */
 var g_HasRejoined = false;
 
+/**
+ * Shows a message box asking the user to leave if "won" or "defeated".
+ */
+var g_ConfirmExit = false;
+
 /**
  * True if the current player has paused the game explicitly.
  */
@@ -118,17 +123,6 @@ var g_TemplateData = {};
 var g_TemplateDataWithoutLocalization = {};
 var g_TechnologyData = {};
 
-/**
- * Cache concatenated list of player states ("active", "defeated" or "won").
- */
-var g_CachedLastStates = "";
-
-/**
- * Whether the current player has lost/won and reached the end of their game.
- * Used for reporting the gamestate and showing the game-end message only once.
- */
-var g_GameEnded = false;
-
 /**
  * Top coordinate of the research list.
  * Changes depending on the number of displayed counters.
@@ -240,8 +234,6 @@ function init(initData, hotloadData)
 		g_ReplaySelectionData = initData.replaySelectionData;
 		g_HasRejoined = initData.isRejoining;
 
-		g_Players = getPlayerData();
-
 		if (initData.savedGUIData)
 			restoreSavedGameData(initData.savedGUIData);
 
@@ -251,15 +243,14 @@ function init(initData, hotloadData)
 	{
 		if (g_IsReplay)
 			g_PlayerAssignments.local.player = -1;
-
-		g_Players = getPlayerData();
 	}
 
+	g_Players = getPlayerData();
+
 	g_CivData = loadCivData();
 	g_CivData.gaia = { "Code": "gaia", "Name": translate("Gaia") };
 
 	initializeMusic(); // before changing the perspective
-	selectViewPlayer(g_ViewedPlayer);
 
 	let gameSpeed = Engine.GetGUIObjectByName("gameSpeed");
 	gameSpeed.list = g_GameSpeeds.Title;
@@ -281,10 +272,12 @@ function init(initData, hotloadData)
 		playerNames.push(colorizePlayernameHelper("■", player) + " " + g_Players[player].name);
 	}
 
+	// Select "observer" item when rejoining as a defeated player
+	let viewedPlayer = g_Players[Engine.GetPlayerID()];
 	let viewPlayerDropdown = Engine.GetGUIObjectByName("viewPlayer");
 	viewPlayerDropdown.list = playerNames;
 	viewPlayerDropdown.list_data = playerIDs;
-	viewPlayerDropdown.selected = Engine.GetPlayerID() + 1;
+	viewPlayerDropdown.selected = viewedPlayer && viewedPlayer.state == "defeated" ? 0 : Engine.GetPlayerID() + 1;
 
 	// If in Atlas editor, disable the exit button
 	if (Engine.IsAtlasRunning())
@@ -434,6 +427,31 @@ function controlsPlayer(playerID)
 		playerState.state != "defeated" || playerState.controlsAll);
 }
 
+/**
+ * Called when a player has won or was defeated.
+ */
+function playerFinished(player, won)
+{
+	reportGame();
+	updateDiplomacy();
+	updateChatAddressees();
+
+	if (player != Engine.GetPlayerID() || Engine.IsAtlasRunning())
+		return;
+
+	global.music.setState(
+		won ?
+			global.music.states.VICTORY :
+			global.music.states.DEFEAT
+	);
+
+	// Select "observer" item
+	if (!won)
+		Engine.GetGUIObjectByName("viewPlayer").selected = 0;
+
+	g_ConfirmExit = won ? "won" : "defeated";
+}
+
 /**
  * Sets civ icon for the currently viewed player.
  * Hides most gui objects for observers.
@@ -492,8 +510,6 @@ function resignGame(leaveGameAfterResign)
 		"resign": true
 	});
 
-	updateTopPanel();
-
 	global.music.setState(global.music.states.DEFEAT);
 
 	if (!leaveGameAfterResign)
@@ -582,8 +598,6 @@ function onTick()
 	let tickLength = new Date() - lastTickTime;
 	lastTickTime = now;
 
-	checkPlayerState();
-
 	handleNetMessages();
 
 	updateCursorAndTooltip();
@@ -609,71 +623,6 @@ function onTick()
 	Engine.GuiInterfaceCall("ClearRenamedEntities");
 }
 
-function checkPlayerState()
-{
-	if (g_GameEnded || Engine.GetPlayerID() < 1)
-		return;
-
-	// Send a game report for each player in this game.
-	let m_simState = GetSimState();
-	let playerState = m_simState.players[Engine.GetPlayerID()];
-	let tempStates = "";
-	for (let player of m_simState.players)
-		tempStates += player.state + ",";
-
-	if (g_CachedLastStates != tempStates)
-	{
-		g_CachedLastStates = tempStates;
-		reportGame();
-	}
-
-	if (playerState.state == "active")
-		return;
-
-	// Make sure nothing is open to avoid stacking.
-	closeOpenDialogs();
-
-	// Make sure this doesn't run again.
-	g_GameEnded = true;
-
-	// Select observermode
-	Engine.GetGUIObjectByName("viewPlayer").selected = playerState.state == "won" ? g_ViewedPlayer + 1 : 0;
-
-	let btCaptions;
-	let btCode;
-	let message;
-	let title;
-	if (Engine.IsAtlasRunning())
-	{
-		// If we're in Atlas, we can't leave the game
-		btCaptions = [translate("OK")];
-		btCode = [null];
-		message = translate("Press OK to continue");
-	}
-	else
-	{
-		btCaptions = [translate("No"), translate("Yes")];
-		btCode = [null, leaveGame];
-		message = translate("Do you want to quit?");
-	}
-
-	if (playerState.state == "defeated")
-	{
-		title = translate("DEFEATED!");
-		global.music.setState(global.music.states.DEFEAT);
-	}
-	else if (playerState.state == "won")
-	{
-		title = translate("VICTORIOUS!");
-		global.music.setState(global.music.states.VICTORY);
-		// TODO: Reveal map directly instead of this silly proxy.
-		if (!Engine.GetGUIObjectByName("devCommandsRevealMap").checked)
-			Engine.GetGUIObjectByName("devCommandsRevealMap").checked = true;
-	}
-
-	messageBox(400, 200, message, title, btCaptions, btCode);
-}
-
 function changeGameSpeed(speed)
 {
 	if (!g_IsNetworked)
@@ -714,8 +663,39 @@ function onSimulationUpdate()
 		return;
 
 	handleNotifications();
-
 	updateGUIObjects();
+
+	if (g_ConfirmExit)
+		confirmExit();
+}
+
+/**
+ * Don't show the message box before all playerstate changes are processed.
+ */
+function confirmExit()
+{
+	closeOpenDialogs();
+
+	let subject = g_ConfirmExit == "won" ?
+		translate("You have won!") :
+		translate("You have been defeated!");
+
+	subject += "\n" + translate("Do you want to quit?");
+
+	if (g_IsNetworked && g_IsController)
+		subject += "\n" + translate("Leaving will disconnect all other players.");
+
+	messageBox(
+		400, 200,
+		subject,
+		g_ConfirmExit == "won" ?
+			translate("VICTORIOUS!") :
+			translate("DEFEATED!"),
+		[translate("No"), translate("Yes")],
+		[resumeGame, leaveGame]
+	);
+
+	g_ConfirmExit = false;
 }
 
 function updateGUIObjects()
@@ -747,7 +727,7 @@ function updateGUIObjects()
 		Engine.GetGUIObjectByName("devControlAll").checked = g_DevSettings.controlAll;
 	}
 
-	if (g_ViewedPlayer != -1 && !g_GameEnded)
+	if (!g_IsObserver)
 	{
 		// Update music state on basis of battle state.
 		let battleState = Engine.GuiInterfaceCall("GetBattleState", g_ViewedPlayer);
@@ -805,7 +785,6 @@ function updateGUIStatusBar(nameOfBar, points, maxPoints, direction)
 	statusBar.size = healthSize;
 }
 
-
 function updateHeroes()
 {
 	let playerState = GetSimState().players[g_ViewedPlayer];
@@ -1119,7 +1098,10 @@ function playAmbient()
 
 function getBuildString()
 {
-	return sprintf(translate("Build: %(buildDate)s (%(revision)s)"), { "buildDate": Engine.GetBuildTimestamp(0), revision: Engine.GetBuildTimestamp(2) });
+	return sprintf(translate("Build: %(buildDate)s (%(revision)s)"), {
+		"buildDate": Engine.GetBuildTimestamp(0),
+		"revision": Engine.GetBuildTimestamp(2)
+	});
 }
 
 function showTimeWarpMessageBox()
@@ -1137,7 +1119,8 @@ function showTimeWarpMessageBox()
 function reportGame()
 {
 	// Only 1v1 games are rated (and Gaia is part of g_Players)
-	if (!Engine.HasXmppClient() || !Engine.IsRankedGame() || g_Players.length != 3)
+	if (!Engine.HasXmppClient() || !Engine.IsRankedGame() ||
+	    g_Players.length != 3 || Engine.GetPlayerID() == -1)
 		return;
 
 	let extendedSimState = Engine.GuiInterfaceCall("GetExtendedSimulationState");
diff --git a/binaries/data/mods/public/maps/scripts/ConquestCommon.js b/binaries/data/mods/public/maps/scripts/ConquestCommon.js
index 1f4c92276b..b118216ae1 100644
--- a/binaries/data/mods/public/maps/scripts/ConquestCommon.js
+++ b/binaries/data/mods/public/maps/scripts/ConquestCommon.js
@@ -25,8 +25,12 @@ Trigger.prototype.ConquestHandlerOwnerShipChanged = function(msg)
 	if (index >= 0)
 	{
 		entities.splice(index, 1);
-		if (!entities.length && Engine.QueryInterface(this.conquestEntitiesByPlayer[msg.from].player, IID_Player).GetState() == "active")
-			Engine.PostMessage(this.conquestEntitiesByPlayer[msg.from].player, MT_PlayerDefeated, { "playerId": msg.from } );
+		if (!entities.length)
+		{
+			let cmpPlayer = QueryPlayerIDInterface(msg.from);
+			if (cmpPlayer)
+				cmpPlayer.SetState("defeated");
+		}
 	}
 }
 
@@ -67,7 +71,7 @@ Trigger.prototype.ConquestTrainingFinished = function(msg)
 		return;	
 	}
 	this.conquestEntitiesByPlayer[player].entities.push(...msg.entities);
-}
+};
 
 Trigger.prototype.ConquestStartGameCount = function()
 {
@@ -90,7 +94,7 @@ Trigger.prototype.ConquestStartGameCount = function()
 	});
 
 	this.conquestDataInit = true;
-}
+};
 
 var cmpTrigger = Engine.QueryInterface(SYSTEM_ENTITY, IID_Trigger);
 
diff --git a/binaries/data/mods/public/maps/scripts/TriggerHelper.js b/binaries/data/mods/public/maps/scripts/TriggerHelper.js
index 031739e15e..0b7955e55c 100644
--- a/binaries/data/mods/public/maps/scripts/TriggerHelper.js
+++ b/binaries/data/mods/public/maps/scripts/TriggerHelper.js
@@ -114,7 +114,8 @@ TriggerHelper.GetResourceType = function(entity)
 }; 
 
 /**
- * Wins the game for a player
+ * The given player will win the game.
+ * If it's not a last man standing game, then allies will win too.
  */
 TriggerHelper.SetPlayerWon = function(playerID)
 {
@@ -127,10 +128,9 @@ TriggerHelper.SetPlayerWon = function(playerID)
  */
 TriggerHelper.DefeatPlayer = function(playerID)
 {
-	let cmpPlayerManager = Engine.QueryInterface(SYSTEM_ENTITY, IID_PlayerManager);
-	let playerEnt = cmpPlayerManager.GetPlayerByID(playerID);
-
-	Engine.PostMessage(playerEnt, MT_PlayerDefeated, { "playerId": playerID } );
+	let cmpPlayer = QueryPlayerIDInterface(playerID);
+	if (cmpPlayer)
+		cmpPlayer.SetState("defeated");
 };
 
 /**
diff --git a/binaries/data/mods/public/simulation/components/EndGameManager.js b/binaries/data/mods/public/simulation/components/EndGameManager.js
index 502b6fc0bb..ccf4ee1f4e 100644
--- a/binaries/data/mods/public/simulation/components/EndGameManager.js
+++ b/binaries/data/mods/public/simulation/components/EndGameManager.js
@@ -1,6 +1,6 @@
 /**
- * System component which regularly checks victory/defeat conditions
- * and if they are satisfied then it marks the player as victorious/defeated.
+ * System component to store the gametype, gametype settings and
+ * check for allied victory / last-man-standing.
  */
 function EndGameManager() {}
 
@@ -19,6 +19,10 @@ EndGameManager.prototype.Init = function()
 	// False for a "last man standing" game
 	this.alliedVictory = true;
 
+	// Don't do any checks before the diplomacies were set for each player
+	// or when marking a player as won.
+	this.skipAlliedVictoryCheck = true;
+
 	this.lastManStandingMessage = undefined;
 };
 
@@ -41,6 +45,7 @@ EndGameManager.prototype.SetGameType = function(newGameType, newSettings = {})
 {
 	this.gameType = newGameType;
 	this.gameTypeSettings = newSettings;
+	this.skipAlliedVictoryCheck = false;
 
 	Engine.BroadcastMessage(MT_GameTypeChanged, {});
 };
@@ -50,26 +55,20 @@ EndGameManager.prototype.MarkPlayerAsWon = function(playerID)
 	let cmpPlayerManager = Engine.QueryInterface(SYSTEM_ENTITY, IID_PlayerManager);
 	let numPlayers = cmpPlayerManager.GetNumPlayers();
 
-	for (let i = 1; i < numPlayers; ++i)
-	{
-		let playerEntityId = cmpPlayerManager.GetPlayerByID(i);
-		let cmpPlayer = Engine.QueryInterface(playerEntityId, IID_Player);
+	this.skipAlliedVictoryCheck = true;
 
-		if (cmpPlayer.GetState() != "active")
-			continue;
+	// Group win/defeat messages
+	for (let won of [false, true])
+		for (let i = 1; i < numPlayers; ++i)
+		{
+			let cmpPlayer = QueryPlayerIDInterface(i);
+			let hasWon = playerID == i || this.alliedVictory && cmpPlayer.IsMutualAlly(playerID);
 
-		if (playerID == cmpPlayer.GetPlayerID() || this.alliedVictory && cmpPlayer.IsMutualAlly(playerID))
-			cmpPlayer.SetState("won");
-		else
-			Engine.PostMessage(playerEntityId, MT_PlayerDefeated, {
-				"playerId": i,
-				"skipAlliedVictoryCheck": true
-			});
-	}
+			if (hasWon == won)
+				cmpPlayer.SetState(won ? "won" : "defeated");
+		}
 
-	// Reveal the map to all players
-	let cmpRangeManager = Engine.QueryInterface(SYSTEM_ENTITY, IID_RangeManager);
-	cmpRangeManager.SetLosRevealAll(-1, true);
+	this.skipAlliedVictoryCheck = false;
 };
 
 EndGameManager.prototype.SetAlliedVictory = function(flag)
@@ -79,6 +78,9 @@ EndGameManager.prototype.SetAlliedVictory = function(flag)
 
 EndGameManager.prototype.AlliedVictoryCheck = function()
 {
+	if (this.skipAlliedVictoryCheck)
+		return;
+
 	let cmpGuiInterface = Engine.QueryInterface(SYSTEM_ENTITY, IID_GuiInterface);
 	let cmpPlayerManager = Engine.QueryInterface(SYSTEM_ENTITY, IID_PlayerManager);
 	if (!cmpGuiInterface || !cmpPlayerManager)
@@ -101,18 +103,12 @@ EndGameManager.prototype.AlliedVictoryCheck = function()
 	}
 
 	if (this.alliedVictory || allies.length == 1)
-	{
 		for (let playerID of allies)
 		{
 			let cmpPlayer = QueryPlayerIDInterface(playerID);
 			if (cmpPlayer)
 				cmpPlayer.SetState("won");
 		}
-
-		let cmpRangeManager = Engine.QueryInterface(SYSTEM_ENTITY, IID_RangeManager);
-		if (cmpRangeManager)
-			cmpRangeManager.SetLosRevealAll(-1, true);
-	}
 	else
 		this.lastManStandingMessage = cmpGuiInterface.AddTimeNotification({
 			"message": markForTranslation("Last remaining player wins."),
@@ -127,14 +123,12 @@ EndGameManager.prototype.OnInitGame = function(msg)
 
 EndGameManager.prototype.OnGlobalDiplomacyChanged = function(msg)
 {
-	if (!msg.skipAlliedVictoryCheck)
-		this.AlliedVictoryCheck();
+	this.AlliedVictoryCheck();
 };
 
 EndGameManager.prototype.OnGlobalPlayerDefeated = function(msg)
 {
-	if (!msg.skipAlliedVictoryCheck)
-		this.AlliedVictoryCheck();
+	this.AlliedVictoryCheck();
 };
 
 Engine.RegisterSystemComponentType(IID_EndGameManager, "EndGameManager", EndGameManager);
diff --git a/binaries/data/mods/public/simulation/components/Player.js b/binaries/data/mods/public/simulation/components/Player.js
index bc98d200fe..4f81bd6254 100644
--- a/binaries/data/mods/public/simulation/components/Player.js
+++ b/binaries/data/mods/public/simulation/components/Player.js
@@ -359,9 +359,62 @@ Player.prototype.GetState = function()
 	return this.state;
 };
 
-Player.prototype.SetState = function(newState)
+Player.prototype.SetState = function(newState, resign)
 {
+	if (this.state != "active")
+		return;
+
+	if (newState != "won" && newState != "defeated")
+	{
+		warn("Can't change playerstate to " + this.state);
+		return;
+	}
+
 	this.state = newState;
+
+	let won = newState == "won";
+
+	// Reveal map to all or only that player
+	let cmpRangeManager = Engine.QueryInterface(SYSTEM_ENTITY, IID_RangeManager);
+	cmpRangeManager.SetLosRevealAll(won ? -1 : this.playerID, true);
+
+	if (!won)
+	{
+		// Reassign all player's entities to Gaia
+		let entities = cmpRangeManager.GetEntitiesByPlayer(this.playerID);
+
+		// The ownership change is done in two steps so that entities don't hit idle
+		// (and thus possibly look for "enemies" to attack) before nearby allies get
+		// converted to Gaia as well.
+		for (let entity of entities)
+		{
+			let cmpOwnership = Engine.QueryInterface(entity, IID_Ownership);
+			cmpOwnership.SetOwnerQuiet(0);
+		}
+
+		// With the real ownership change complete, send OwnershipChanged messages.
+		for (let entity of entities)
+			Engine.PostMessage(entity, MT_OwnershipChanged, {
+				"entity": entity,
+				"from": this.playerID,
+				"to": 0
+			});
+	}
+
+	Engine.BroadcastMessage(won ? MT_PlayerWon : MT_PlayerDefeated, { "playerId": this.playerID });
+
+	let cmpGUIInterface = Engine.QueryInterface(SYSTEM_ENTITY, IID_GuiInterface);
+	if (won)
+		cmpGUIInterface.PushNotification({
+			"type": "won",
+			"players": [this.playerID]
+		});
+	else
+		cmpGUIInterface.PushNotification({
+			"type": "defeat",
+			"players": [this.playerID],
+			"resign": resign
+		});
 };
 
 Player.prototype.GetTeam = function()
@@ -369,7 +422,7 @@ Player.prototype.GetTeam = function()
 	return this.team;
 };
 
-Player.prototype.SetTeam = function(team, skipAlliedVictoryCheck = false)
+Player.prototype.SetTeam = function(team)
 {
 	if (this.teamsLocked)
 		return;
@@ -385,14 +438,13 @@ Player.prototype.SetTeam = function(team, skipAlliedVictoryCheck = false)
 			if (this.team != cmpPlayer.GetTeam())
 				continue;
 
-			this.SetAlly(i, skipAlliedVictoryCheck);
-			cmpPlayer.SetAlly(this.playerID, skipAlliedVictoryCheck);
+			this.SetAlly(i);
+			cmpPlayer.SetAlly(this.playerID);
 		}
 
 	Engine.BroadcastMessage(MT_DiplomacyChanged, {
 		"player": this.playerID,
-		"otherPlayer": null,
-		"skipAlliedVictoryCheck": skipAlliedVictoryCheck
+		"otherPlayer": null
 	});
 };
 
@@ -411,18 +463,17 @@ Player.prototype.GetDiplomacy = function()
 	return this.diplomacy;
 };
 
-Player.prototype.SetDiplomacy = function(dipl, skipAlliedVictoryCheck = false)
+Player.prototype.SetDiplomacy = function(dipl)
 {
 	this.diplomacy = dipl;
 
 	Engine.BroadcastMessage(MT_DiplomacyChanged, {
 		"player": this.playerID,
-		"otherPlayer": null,
-		"skipAlliedVictoryCheck": skipAlliedVictoryCheck
+		"otherPlayer": null
 	});
 };
 
-Player.prototype.SetDiplomacyIndex = function(idx, value, skipAlliedVictoryCheck = false)
+Player.prototype.SetDiplomacyIndex = function(idx, value)
 {
 	let cmpPlayer = QueryPlayerIDInterface(idx);
 	if (!cmpPlayer)
@@ -435,13 +486,12 @@ Player.prototype.SetDiplomacyIndex = function(idx, value, skipAlliedVictoryCheck
 
 	Engine.BroadcastMessage(MT_DiplomacyChanged, {
 		"player": this.playerID,
-		"otherPlayer": cmpPlayer.GetPlayerID(),
-		"skipAlliedVictoryCheck": skipAlliedVictoryCheck
+		"otherPlayer": cmpPlayer.GetPlayerID()
 	});
 
 	// Mutual worsening of relations
 	if (cmpPlayer.diplomacy[this.playerID] > value)
-		cmpPlayer.SetDiplomacyIndex(this.playerID, value, skipAlliedVictoryCheck);
+		cmpPlayer.SetDiplomacyIndex(this.playerID, value);
 };
 
 Player.prototype.UpdateSharedLos = function()
@@ -520,9 +570,9 @@ Player.prototype.IsAI = function()
 	return this.isAI;
 };
 
-Player.prototype.SetAlly = function(id, skipAlliedVictoryCheck = false)
+Player.prototype.SetAlly = function(id)
 {
-	this.SetDiplomacyIndex(id, 1, skipAlliedVictoryCheck);
+	this.SetDiplomacyIndex(id, 1);
 };
 
 /**
@@ -558,9 +608,9 @@ Player.prototype.IsExclusiveMutualAlly = function(id)
 	return this.playerID != id && this.IsMutualAlly(id);
 };
 
-Player.prototype.SetEnemy = function(id, skipAlliedVictoryCheck = false)
+Player.prototype.SetEnemy = function(id)
 {
-	this.SetDiplomacyIndex(id, -1, skipAlliedVictoryCheck);
+	this.SetDiplomacyIndex(id, -1);
 };
 
 /**
@@ -583,9 +633,9 @@ Player.prototype.IsEnemy = function(id)
 	return this.diplomacy[id] < 0;
 };
 
-Player.prototype.SetNeutral = function(id, skipAlliedVictoryCheck = false)
+Player.prototype.SetNeutral = function(id)
 {
-	this.SetDiplomacyIndex(id, 0, skipAlliedVictoryCheck);
+	this.SetDiplomacyIndex(id, 0);
 };
 
 /**
@@ -649,43 +699,6 @@ Player.prototype.OnGlobalOwnershipChanged = function(msg)
 	}
 };
 
-Player.prototype.OnPlayerDefeated = function(msg)
-{
-	this.state = "defeated";
-
-	// Reassign all player's entities to Gaia
-	var cmpRangeManager = Engine.QueryInterface(SYSTEM_ENTITY, IID_RangeManager);
-	var entities = cmpRangeManager.GetEntitiesByPlayer(this.playerID);
-
-	// The ownership change is done in two steps so that entities don't hit idle
-	// (and thus possibly look for "enemies" to attack) before nearby allies get
-	// converted to Gaia as well.
-	for (var entity of entities)
-	{
-		var cmpOwnership = Engine.QueryInterface(entity, IID_Ownership);
-		cmpOwnership.SetOwnerQuiet(0);
-	}
-
-	// With the real ownership change complete, send OwnershipChanged messages.
-	for (var entity of entities)
-		Engine.PostMessage(entity, MT_OwnershipChanged, {
-			"entity": entity,
-			"from": this.playerID,
-			"to": 0
-		});
-
-	// Reveal the map for this player.
-	cmpRangeManager.SetLosRevealAll(this.playerID, true);
-
-	// Send a chat message notifying of the player's defeat.
-	var cmpGUIInterface = Engine.QueryInterface(SYSTEM_ENTITY, IID_GuiInterface);
-	cmpGUIInterface.PushNotification({
-		"type": "defeat",
-		"players": [this.playerID],
-		"resign": !!msg.resign
-	});
-};
-
 Player.prototype.OnResearchFinished = function(msg)
 {
 	if (msg.tech == this.template.SharedLosTech)
diff --git a/binaries/data/mods/public/simulation/components/PlayerManager.js b/binaries/data/mods/public/simulation/components/PlayerManager.js
index 98ce644f2e..a9f898e28e 100644
--- a/binaries/data/mods/public/simulation/components/PlayerManager.js
+++ b/binaries/data/mods/public/simulation/components/PlayerManager.js
@@ -23,7 +23,7 @@ PlayerManager.prototype.AddPlayer = function(ent)
 		newDiplo[i] = -1;
 	}
 	newDiplo[id] = 1;
-	cmpPlayer.SetDiplomacy(newDiplo, true);
+	cmpPlayer.SetDiplomacy(newDiplo);
 	
 	return id;
 };
diff --git a/binaries/data/mods/public/simulation/components/interfaces/EndGameManager.js b/binaries/data/mods/public/simulation/components/interfaces/EndGameManager.js
index ec84ddd9ee..82a126cbca 100644
--- a/binaries/data/mods/public/simulation/components/interfaces/EndGameManager.js
+++ b/binaries/data/mods/public/simulation/components/interfaces/EndGameManager.js
@@ -1,3 +1,4 @@
 Engine.RegisterInterface("EndGameManager");
 Engine.RegisterMessageType("PlayerDefeated");
+Engine.RegisterMessageType("PlayerWon");
 Engine.RegisterMessageType("GameTypeChanged");
diff --git a/binaries/data/mods/public/simulation/helpers/Cheat.js b/binaries/data/mods/public/simulation/helpers/Cheat.js
index f3164db5e3..0624478afa 100644
--- a/binaries/data/mods/public/simulation/helpers/Cheat.js
+++ b/binaries/data/mods/public/simulation/helpers/Cheat.js
@@ -48,10 +48,9 @@ function Cheat(input)
 		}
 		return;
 	case "defeatplayer":
-		var playerEnt = cmpPlayerManager.GetPlayerByID(input.parameter);
-		if (playerEnt == INVALID_ENTITY)
-			return;
-		Engine.PostMessage(playerEnt, MT_PlayerDefeated, { "playerId": input.parameter });
+		cmpPlayer = QueryPlayerIDInterface(input.parameter);
+		if (cmpPlayer)
+			cmpPlayer.SetState("defeated");
 		return;
 	case "createunits":
 		var cmpProductionQueue = input.selected.length && Engine.QueryInterface(input.selected[0], IID_ProductionQueue);
diff --git a/binaries/data/mods/public/simulation/helpers/Commands.js b/binaries/data/mods/public/simulation/helpers/Commands.js
index 5ccb3a957c..fba68fed70 100644
--- a/binaries/data/mods/public/simulation/helpers/Commands.js
+++ b/binaries/data/mods/public/simulation/helpers/Commands.js
@@ -414,8 +414,9 @@ var g_Commands = {
 
 	"defeat-player": function(player, cmd, data)
 	{
-		// Send "OnPlayerDefeated" message to player
-		Engine.PostMessage(data.playerEnt, MT_PlayerDefeated, { "playerId": player, "resign": !!cmd.resign });
+		let cmpPlayer = QueryPlayerIDInterface(player);
+		if (cmpPlayer)
+			cmpPlayer.SetState("defeated", !!cmd.resign);
 	},
 
 	"garrison": function(player, cmd, data)
diff --git a/binaries/data/mods/public/simulation/helpers/Player.js b/binaries/data/mods/public/simulation/helpers/Player.js
index 951a457759..833176f059 100644
--- a/binaries/data/mods/public/simulation/helpers/Player.js
+++ b/binaries/data/mods/public/simulation/helpers/Player.js
@@ -123,7 +123,7 @@ function LoadPlayerSettings(settings, newPlayers)
 
 		// If diplomacy explicitly defined, use that; otherwise use teams
 		if (getSetting(playerData, playerDefaults, i, "Diplomacy") !== undefined)
-			cmpPlayer.SetDiplomacy(getSetting(playerData, playerDefaults, i, "Diplomacy"), true);
+			cmpPlayer.SetDiplomacy(getSetting(playerData, playerDefaults, i, "Diplomacy"));
 		else
 		{
 			// Init diplomacy
@@ -137,7 +137,7 @@ function LoadPlayerSettings(settings, newPlayers)
 				else
 					cmpPlayer.SetEnemy(j);
 			}
-			cmpPlayer.SetTeam(myTeam === undefined ? -1 : myTeam, true);
+			cmpPlayer.SetTeam(myTeam === undefined ? -1 : myTeam);
 		}
 
 		// If formations explicitly defined, use that; otherwise use civ defaults