How can nationalism lead to war?

Ineed with what i should write for my research paper. my topic is history of slavery. 1800 words. all i need is what to write in each paragraphs. like when the research paper has titles for each paragraph and it explains the tile in each paragraph. for example when did slaverh begin? why did it begin like an outline.

Why didn’t the united states participate in the league of nations? the u.s. senate did not want the country to join. president wilson did not want the country to join. the league of nations was only for european countries. the league of nations had failed to prevent world war 1

How did philip ii view the religious rights of protestant citizens in his empire