Both Marcus Garvey’s UNIA and the KKK were nationalist organization in the United States. They were both helped to prominence in the 1920s by some of the same factors.
In the international arena, one of the major causes of their rise was World War I. Another was the rise of radical ideas such as socialism and anarchism in Europe. Both of these influenced events in the United States which, in turn, influenced the rise of these organizations.
World War I influenced the rise of these groups largely through the fact that it caused the movement of many African Americans to the North. It also helped expose some African Americans to influences from outside the country. This led African Americans to form more of a sense of nationalism and of pride. This helped bring about the rise of UNIA.
The rise of radical ideas influenced the United States because they came to the country with European immigrants. The rise of these ideas helped to make white nationalists feel that their country was being taken over by alien forces. This helped lead to the rise of the KKK.