what you said the MC kinda explained in page 21
He prevented Anastasia's condemnation and banishment which resulted in the civil war not happening thus preventing the invasion
Kinda stupid of trash prince to do it in the original timeline but I guess its for plot purposes.....so backing or not he will go after the MC and his loved ones cuz he can lol until he gets caught and condemned by the king himself
someone correct me if I'm wrong,
but in original story, the Prince that MC defeated, never really planned for Anastasia to be sexually assaulted by bandits. he didn't care really, also Amy in original game was actually a kind person but naive of the situation.
The Prince sold Anastasia to the neighboring country's Prince secretly by arranging for her to be kidnapped in return for some favor or something i don't remember.
it was the neighboring country's prince's plan for his kidnapping to be halfway attacked by bandits group who would all assault Anastasia until they basically mind break her so that he can then give her some cursed sword that fit her Ice power to control her and make her into a weapon of mass destruction, who become one of the game's final boss.
this was the original plot in the game that was explained to us early on in the webnovel.