Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.
The reason there is no World War Two in Tanya's new world is that...
...Tanya found and killed Adolf Hitler (in a manner similar to how she arranged for the deaths of Harald and Kurst), who was, just like his Real Life-counterpart, a lance corporal fighting in the war (This WMG was inspired by this fanfiction story
). Such an outcome may very well be what "Being X" planned all along, feeling guilty for not preventing World War Two with all its bloodshed and horrors in our world. The reason the exploits of Tanya are effectively redacted and she is recorded in history only as the "Eleventh Goddess" is because Tanya became a Saint
Despite her side losing the war, Tanya was later canonized as a saint by the local religion. To hide her violent past, the church leaned on all combatants to effectively erase Tanya from history leaving only the tales of the miraculous Eleventh Goddess to serve as an inspiration for future generations. For Being X it all went Just as Planned.... The reason the Empire surrendered is because...
- Tanya had either died or gone missing. There is much made about how Tanya is becoming crucial for Imperial morale. The manga especially highlights this as many individuals get taken in by her legend. When Tanya was martyred in battle, the effect was devastating and led the Empire to sign an armistice rather than continue fighting.
- Alternatively, the Empire surrendered out of necessity to defeat Being X, not because they were losing. It is heavily implied in the light novel that Being X instigated the Federation to invade the Empire. A further inference is that this world war is what Being X actually wants. Tanya might eventually have realised this and then found a way to end the war. This would explain why everything about Tanya is classified after the war, on both the Imperial side and the Allied side - nobody wants to publicly acknowledge the existence of Being X or that they were manipulated into a war of such a destructive scale.
Tanya is an earlier incarnation of Ciaphas Cain
The similarities between the two are striking:- Both are sociopaths but are less sociopathic than they think they are.
- Both want nice, safe, comfortable lives in the rear but instead are on the front lines.
- Both describe themselves as cowards and describe some of their braver actions in terms of cowardice.
- Both respond to others in a way that make people think they want to be in the thick of battle.
- Both justify suppressing the urge to run away in terms of protecting their careers, of avoiding a firing squad or both.
- Both are skilled at commanding troops and in personal combat.
- Neither are willing to lead or order troops into massacres and both justify the need to avoid unnecessary casualties in terms of needing a "meat shield".
- Both actually feel bad when they lose troops under their command.
