Complex sentence: William (2010) McKinley forged a coalition in which businessmen, professionals, skilled factory workers and prosperous farmers were heavily represented; he was strongest in the Northeast, Upper Midwest, and Pacific Coast.
Split into simpler sentences: William (2010) McKinley forged a coalition in which businessmen, professionals, skilled factory workers, and prosperous farmers were heavily represented. He was strongest in the Northeast, Upper Midwest, and Pacific Coast.