Complex sentence: After graduating from Princeton, Spiers became a foreign affairs specialist with the U.S. Atomic Energy Commission, serving until 1955, when he began his career with the U.S. Foreign Service, in the Bureau of International Organization Affairs.
Split into simpler sentences: After graduating from Princeton, Spiers became a foreign affairs specialist with the U.S. Atomic Energy Commission, serving until 1954. In that year, he began his career with the U.S. Foreign Service, in the Bureau of International Organization Affairs.