Complex sentence: He founded a small Catholic resistance group and sought to amalgamate into one organised band the Christians, Communists and trade unionists against the Nazis, and as a soldier later came into contact with the resistance group "Soldatenrat".
Split into simpler sentences: He founded a small Catholic resistance group and sought to amalgamate into one organised band the Christians, Communists and trade unionists against the Nazis. As a soldier, he later came into contact with the resistance group "Soldatenrat".