Complex sentence: In the U.S., Sonnenfeldt finished high school, was drafted into the U.S. Army, became a U.S. citizen was sent back to Europe as a U.S. soldier.
Split into simpler sentences: In the U.S., Sonnenfeldt finished high school, was drafted into the U.S. Army, and became a U.S. citizen. He was then sent back to Europe as a U.S. soldier.