Why did so many race riots / race massacres occur during and immediately after WWI?

Political rights for women grew most rapidly on the western frontier primarily because (1) the settlers were influenced by native american indian societies (2) women greatly outnumbered men in the west (3) pioneer life often required men and women to share responsibilities equally (4) immigrants settling in the west brought ideals of gender equality from europe

By the end of the 1800s, there was a change in the nature of the immigrants coming to the united states. immigration from northern europe—england, ireland, germany, and scandinavia—declined, while immigration from italy, russia, and austria-hungary grew. in fact, between 1900 and 1910, more than three-fourths of all immigrants came from these three countries. unfortunately, these countries were far removed england, the home of our founders, and the immigrants who came from them had a hard time adjusting to life in their new country.

Space is not completely empty. there are small particles in space. what happens when these particles come together?