Complex sentence: The army dropped its responsibility for schooling at the war's end, but the American Missionary Association needed teachers, and Ruby worked for them in New Orleans, and, when the Freedmen's Bureau schools started up, became a teacher there.
Split into simpler sentences: The army dropped its responsibility for schooling at the war's end. The American Missionary Association needed teachers, and Ruby worked for them in New Orleans, and, when the Freedmen's Bureau schools started up, became a teacher there.