During the World War I, labor unions had promised not to strike in order to support the war effort. With the war over, however, they could strike again!
Laborers went on strike in great numbers. Workers in industries such as steel and coal fought for better working conditions and higher wages.
Meanwhile, the combination of Jim Crow in the South and the economic opportunities in the North encouraged thousands of African-Americans to partake in the Great Migration northward.
These economic opportunities were often due to the numerous strikes. Many African-Americans were hired as "strikebreakers", which meant they were hired by companies in place of striking workers. This undermined whatever strike was taking place.
The KKK also witnessed a revival at this time, promoting "Americanization" and violent discrimination against anyone who was not a white, Anglo-Saxon Protestant.
This "New KKK" was especially significant because their marches occurred all over the nation, including the North; It was no longer solely in the Jim Crow South.