Why was there an increase in xenophobia after ww1?

Dictionary definitions of xenophobia include: "deep-rooted fear towards foreigners." 

World war one was the first major war between MANY countries.

It created an US versus THEM mentality. People trusted outsiders less and wanted to keep to themselves.

They also wanted their country to be the winning country in future situations. 

Cis wrong and it is a because i said so yaass

The one that considered as a direct result of the presidential committee on civil rights’