Complex sentence: From 1973 to 1974, Spiers was the U.S. Ambassador to the Bahamas; he later returned to London as the Deputy Chief of Mission, keeping this post until 1977.
Split into simpler sentences: From 1973 to 1974, Spiers was the U.S. Ambassador to the Bahamas. He later returned to London as the Deputy Chief of Mission, holding this post until 1977.