Complex sentence: He initially attended Williams College where he was a member of the Kappa Alpha Society and then accepted a nomination to the United States Military Academy where he graduated at the head of his class in 1862 and immediately joined the Union forces already fighting in the Civil War.
Split into simpler sentences: He initially attended Williams College, where he was a member of the Kappa Alpha Society, and then accepted a nomination to the United States Military Academy, where he graduated at the head of his class in 1862. He immediately joined the Union forces already fighting in the Civil War.