I think it was the Three-Fifths compromise
A the progressive era was a period of widespread social activism an political reform across the united states from the 1890s to the 1920s. the movement drew it's ideals and inspiration from the writings of Thomas Jefferson and reform groups that attracted attention in the 19the century. They made many impacts but here are a few. an active government that would take the initiative in reform. more economic and political rights for women. regulation on child labor. direct election of united states senators
The biggest reason why WWII started would be the invasions and attacks towards nations that Hitler imposed also breaking the Treaty of Versailles, the least I would say is the pure justice or judgement between a difference in Nazi ideology and the rest of the world.
1) Invasions / Attacks
2) Broke treaty of Versailles
3) Nazi ideology vs the rest of world
4) Tensions from WWI