As the Crash Course video heavily argued, it is impossible to place the full blame on any one country. A Serbian shot Archduke Frans Ferdinand, but Austria-Hungary was the one to declare war on Serbia, but Germany gave Austria-Hungary a blank check, declared war on Russia and moved through Belgium (which brought Britain into the war), but Russia was the first to mobilize. The US was initially neutral, which is wildly uncharacteristic if you consider America’s global position later in the twentieth century.
I don’t think that you can really blame anyone for World War I. The countries of Europe were itching to show off their military, form alliances, practice imperialism and boost nationalism. Apparently a war was the best way to do this. One of the most surprising things was how little the United States wanted to do with it at first.
Zinn describes how President Woodrow Wilson had promised that the U.S. would stay neutral. This changed when Germans sunk the Lusitania, which killed Americans, effectively bringing the U.S. into the war (even if the economics were more attractive than avenging the dead Americans). The war was not extraordinarily popular in the United States. W. E. B. Du Bois thought that America was exploiting the world. Most citizens were against the war as well, which prompted the U.S. to pass the Espionage Act (punishing anti-war speech), which more or less stepped on the First Amendment, despite arguments saying that it didn’t.
The world was a mess when the war ended in November of 1918. The U.S. was no exception. Anti-Immigration sentiment was growing even more. A bomb set off in front of the Attorney General’s home only made matters worse, and prompted the government to deport immigrants that were for property destruction. Two Italian immigrants (Nicola Sacco and Bartolomeo Vanzetti) were charged for a murder and executed, with their background (immigrants) leading to their accusation. The war may have helped the economy, but it did not help society.