Chaos Invasion

The Chaos Invasion is an end-game event that occurs in The Old World and Mortal Empires campaigns. It involves the forces of Chaos under Archaon, descending south to attack most other races.
As of the December 3rd update (2020), the Chaos Invasion now has different levels the player can set at the start of a Mortal Empires campaign. These are "On" "Off" "Hard" "Very Hard" and "Legendary". This scales the number of armies spawned during the Chaos Invasion.
The Chaos Invasion does not occur in Immortal Empires, instead it's been replaced by a variety of Endgame scenarios.
== Description ==
The Old World despairs, for Archaon the Everchosen, Champion of Chaos, has come and with him the End Times!
Once a Templar Priest of Sigmar, Archaon uncovered a terrible secret which drove him to reject his faith and pledge himself to the Gods of Chaos. In their service, he has devoted himself to the world's destruction, defeating all challengers and rising to a position of dominance over all in the Chaos Wastes, achieving the ultimate accolade - his dark coronation as the Everchosen; the vessel through which the Dark Gods unite their followers to turn the world into a Realm of Chaos. It is to his banner that the Warriors of Chaos have been flocking, and it is his malign will that now drives them forth in a terrible wave of destruction destined to sweep all before it.
The earth groans beneath the iron-shod feet of Archaon's numberless horde, and with him comes death. Is there any champion of the Old World mighty enough to withstand the Lord of the End Times? 
==Overview==
The invasion can be very destructive. The factions who attack are mostly hordes or similar factions, so they tend to raze a lot of settlements. Additionally, there is a global +2 Chaos Corruption during the invasion.
Factions involved in the invasion:
* Warriors of Chaos are the primary aggressors. In Mortal Empires, these subfactions used to be included but have been removed:
** Puppets of Chaos (Removed)
** Servants to Chaos (Removed)
* Beastmen:
** Warherd of Chaos
* Norsca:
** Bjornling: Respawns alongside the main invasion when fully killed beforehand, always starts neutral with Warriors of Chaos
** Varg: Automatically vassals of the Warriors of Chaos if still on the map
** Skaeling: Automatically vassals of the Warriors of Chaos if still on the map
** All other Norscan factions do not automatically become Vassals, but may ally with Chaos all the same.
Opposing Chaos is The Empire, Dwarfs, Bretonnia and other human factions. In Mortal Empires, they are joined by High Elves and Lizardmen. These factions gain the diplomatic trait Shield of Civilization during a Chaos Invasion, making them more likely to stick together against Chaos.
Greenskins, Vampire Coast, Vampire Counts, Skaven, Dark Elves and Tomb Kings do not gain this trait, though they are automatically at war with the Warriors of Chaos, who will not hesitate to attack them if they get in the way.
Wood Elves will also automatically be at war with the Warriors of Chaos, in addition to having negative diplomatic relations with other Chaos factions, especially Beastmen whom they hate.
Many factions have a campaign victory condition that involves wounding Archaon and dealing with the Warriors of Chaos.
===What happens if I'm playing as the Warriors of Chaos, Norsca, or Beastmen?===
If you are playing as a Norscan faction (World Walkers or Wintertooth), you will get an event called The Everchosen's Summons which allows them to choose to side with Archaon and the Warriors of Chaos, or to side against them and bring about your own invasion. Accepting his summons gives you a faction wide buff. However, this forces the player into war with every faction in game that is not Chaos-aligned, leaving previous ties with other Norscan and/or Beastmen factions intact. If the summon is declined, the Warriors of Chaos will declare war on you, so your next objective is to kill their armies and take their place. Should you successfully defeat them, the player becomes the true Everchosen, and gains a massive faction wide buff.
If you are playing the Warriors of Chaos themselves, you will get an event called The Treachery of Tzeentch; you will still have to fight a rival faction called Chaos Gathering, led by Sarthorael the Everwatcher. In addition, Varg and Skaeling will not automatically be your vassals, but you have the ability to Awaken the Tribes to call addition Norscan Tribes to the map.
If you are playing as any Beastmen tribe, you are not at all summoned to join the Everchosen in his conquest. However, the Warriors of Chaos will not start at war with you. You can choose to aid them and continue your own campaign. You have the option to go to war with them, but there is no real gain from doing this. It is suggested to leave them be and continue your own campaign, potentially helping them if you desire.
==How it plays out==
===Mortal Empires===
* The Chaos Stirs notification indicates the impending arrival of Warriors of Chaos armies.
*The The Rise of Chaos notification indicates the initial spawning of Warriors of Chaos armies in the Chaos Wastes. This occurs between turns 90 and 110. This will spawn 0/4/6/8/12 full Warriors of Chaos stacks. 
* The The Doom Tide notification indicates the additional spawning of Warriors of Chaos armies. It occurs either between turns 140 and 160 or after the player's faction reaches a certain territorial extent (whichever comes first). Four Warriors of Chaos stacks respectively led by Archaon, Sigvald, Kholek, Sarthorael will spawn in the Chaos Wastes, as will a single Warherd of Chaos stack. They will be reinforced by a number of additional stacks, dependent on the setting chosen in the "Chaos Invasion" tab. 
** By default the number is 8, with multipliers of x0/x1/x1.5/x2/x3 for each setting. With the Chaos Invasion set to "Off" there will obviously not be any spawns. With it set to "On", there will be 12 Warriors of Chaos stacks, the four preset ones plus the default addition of 8. By the same token there will be 16 on Hard, 20 on Very Hard, and 28 on Legendary.
** Vassal forces to the Warriors of Chaos will also spawn: aside from the one Warherd of Chaos stack next to the Legendary Lords in the Wastes, four Bjornling stacks will spawn in Norsca (this will be the case even if Bjornling had been eliminated prior). Unlike the Warriors of Chaos, or even their counterparts in the first game, these are not difficulty-dependent; there will always be one Warherd stack and four Bjornling stacks. Skaeling and Varg are vassalized to the Warriors of Chaos by default and may send their own stacks to help, but unlike Bjornling do not receive any new units just from the Chaos Invasion being triggered.
** Naggaroth will get a separate, smaller invasion of 0/4/6/8/12 stacks.
* When Archaon and the Warriors of Chaos are finally defeated for good, the invasion is over. Unless of course, the Warriors of Chaos manage to overwhelm the world. If Archaon, Sigvald, Kholek, and Sarthorael are all killed, the rest of the Warriors of Chaos faction disappears, no matter how many armies they have left.
====The Old World====
* The invasion plays out similarly in the first game's Old World campaign. However, it is smaller in scope and uses a different spawning system, with the number of stacks dependent on regular campaign difficulty rather than a separate Chaos Invasion slider. The details of the Chaos invasion are present in the wh_chaos_invasion.lua file in the game's code. 
** Around turn 80, 3/4/4/5/6 Warriors of Chaos stacks will spawn in the northeast on Easy/Normal/Hard/Very Hard/Legendary. 
** Around turn 130, Chaos armies will start spawning in the Chaos Wastes. The first wave will be 5/5/6/7/8 Warriors of Chaos stacks under generic lords. This wave will be followed by 0/1/2/3/4 waves of the same size. Four of these stacks will be under Archaon, Sigvald, Kholek, and Sarthorael. Thus on Easy there will be a total of 5 Warriors of Chaos stacks (one wave of five), on Normal there will be 10 (two waves of five), on Hard 18 (three waves of six), on Very Hard 28 (four waves of seven), and on Legendary 40 (five waves of eight). 
** On every difficulty the Warriors will be accompanied by multiple Warherd of Chaos stacks (at least three total on Normal). Bjornling, if wiped out, will also respawn in Norsca, and get new armies: 5/5/6/7/8 stacks, equivalent to a single Chaos wave. If it is not wiped out, it still gets the new armies, free of upkeep, and can use both them and its existing forces to join the Chaos Invasion. Varg and Skaeling stacks can also join them, as those factions are vassalized to Chaos by default, but don't get any new spawns.
==Videos==
===Chaos Invasion cinematic===
Category:Total War: Warhammer campaign mode