What is the fine-grained topic of the following text: Friesen was a prominent member of a study commission of four men sent to America by the South Russian Mennonites in 1920 to investigate immigration prospects in either North or South America and also to obtain assistance from American Mennonites for the oppressed Mennonites in Russia. Only return the topic.
Friesen's involvement in a 1920 South Russian Mennonite study commission investigating immigration prospects in America.