Complex sentence: By 1934, Rennie's union with Dorothy Gish was falling to pieces and on October 11,1935 he and Gish divorced and the following year, 1936, he became a naturalized citizen of the United States.
Split into simpler sentences: By 1934, Rennie's union with Dorothy Gish was disintegrating and on October 11,1935 he and Gish divorced. In the following year he became a naturalized citizen of the United States.