Complex sentence: Several groups, in fact, were aggressively supporting U.S. entry into the war and in early fall 1941, when various group activities began to overlap, the Fight for Freedom Committee began exploring a mass merger.
Split into simpler sentences: Several groups, in fact, were aggressively supporting U.S. entry into the war. In early fall 1941, when various group activities began to overlap, the Fight for Freedom Committee began exploring a mass merger.