Complex sentence: The first five-year plan also began to prepare the Soviet Union to win in the Second World War without the initial five-year plan, and the ones that followed, the Soviet Union would not have been prepared for the German invasion in 1941.
Split into simpler sentences: The first five-year plan also began to prepare the Soviet Union to win in the Second World War. Without the initial five-year plan, and the ones that followed, the Soviet Union would not have been prepared for the German invasion in 1941.