Complex sentence: He worked assisting African-Americans who were leaving the South for Kansas as part of the Exoduster Movement of 1879, and in 1881 he was responsible, with Hannibal Carter, for organizing the Freedmen's Oklahoma Immigration Association to promote black homesteading in Oklahoma.
Split into simpler sentences: He worked assisting African-Americans who were leaving the South for Kansas as part of the Exoduster Movement of 1879. In 1881, he was responsible, with Hannibal Carter, for organizing the Freedmen's Oklahoma Immigration Association to promote black homesteading in Oklahoma.