Complex sentence: In 1941, he cofounded the Union for Democratic Action, a group with a strongly militarily interventionist, internationalist foreign policy and a pro-union, liberal domestic policy, and was the group's sole president until its transformation into the Americans for Democratic Action in 1947.
Split into simpler sentences: In 1941, he cofounded the Union for Democratic Action, a group with a strongly militarily interventionist, internationalist foreign policy and a pro-union, liberal domestic policy. He was the group's president until it transformed into the Americans for Democratic Action in 1947.