Complex sentence: Reiley founded the Roosevelt Club in 1901 which had a stated goal of nominating Vice-President Theodore Roosevelt for United States President in the 1904 elections, but the group was disbanded when Roosevelt became President after the assisination of William McKinley in September of that year.
Split into simpler sentences: Reiley founded the Roosevelt Club in 1901 which had a stated goal of nominating Vice-President Theodore Roosevelt for United States President in the 1904 elections. The group was disbanded when Roosevelt became President after the assassination of William McKinley in September of that year.