Create a peace agreement to end either WWI or WWII. This agreement should address the concerns of all of the nations involved and can not be exactly the same as the actual agreement that ended the war.

I don’t know if this is allowed but if it is, you could make changes to the documents. for example, the treaty of versailles (the wwi agreement) said that germany and its allies owed the winning side a lot of money, they had to give back the territory they conquered, and they had to shrink their military. germany wasn’t able to pay the debt, which created more conflict and may have influenced the start of wwii. a change you could make there is making the debts (also called reparations) more reasonable so that while there was a punishment, it could still be paid off in time. that’s just a suggestion, hopefully that helps you :D