Complex sentence: From 1885 to 1886 he was a law clerk at the Department of State, then an Assistant Secretary of State, leaving in 1891 to take the first full professorship of international law at Columbia University; he stayed there until 1924.
Split into simpler sentences: From 1885 to 1886 he was a law clerk at the Department of State, then an Assistant Secretary of State. In 1891 he toke the first full professorship of international law at Columbia University; he stayed there until 1924.