Complex sentence: From 1918 to 1935, Beneš was the first and longest-serving Foreign Minister of Czechoslovakia, a post he held through 10 successive governments, one of which he headed himself from 1921 to 1922.
Split into simpler sentences: From 1918 to 1935, Beneš was the first and longest-serving Foreign Minister of Czechoslovakia. He held the post through 10 successive governments, one of which that he headed himself, from 1921 to 1922.