Complex sentence: In addition, his proposals to free East Germany and normalize relations with the United States alarmed other Politburo members, especially in the wake of the 1953 East German uprising which was put down only after an invasion by Soviet troops.
Split into simpler sentences: In addition, his proposals to free East Germany and normalize relations with the United States alarmed other Politburo members, especially in the wake of the 1953 East German uprising. This was put down only after an invasion by Soviet troops.