Complex sentence: California's involvement in the American Civil War included sending gold east, recruiting volunteer combat units to replace regular forces in territories of the Western United States, maintaining and building numerous camps and fortifications, suppressing secessionist activity and securing the New Mexico Territory against the Confederacy.
Split into simpler sentences: California's involvement in the American Civil War included sending gold east, recruiting volunteer combat units to replace. Regular forces in territories of the Western United States, maintaining and building numerous camps and fortifications, suppressing secessionist activity and securing the New Mexico Territory against the Confederacy.