Answer:
Poverty in poor countries, instability in other countries and revenge for what foreign countries did to their homeland or a specific group or family, inequality is also a major reason, these are all the major reasons I could think off :)
Explanation:
Your answer is: Because President Roosevelt granted the navy permission for U.S. warships to attack German U-boats in self defense.
The planlt valley community
It started with an assassination. The world got angry and war broke out