What effect did the Taiping Rebellion, 1848 revolutions in the Austro-Hungarian Empire, and the assassination of Tsar Alexander II of Russia have on immigration to the United States?

The before mentioned acts were the triggering factor of the First World War. In the early 1920's, the United States congress changed the nation's basic immigration policy. The law of national origins of 1921 not only limited the amount of immigrants that could enter the United States, but also assigned quotas based on national origins, although it should be noted that this country was one of the least affected during the great war.