America became a colonial power in the late 19th century for several reasons: (1) Commercial and business interests in foreign investments and trade expanded dramatically in this period; (2) Military strategists felt overseas territories were important for naval power as described by Alfred Mahan; (3) Social Darwinist thinking, including beliefs of white racial superiority, influenced expansion; (4) Religious missionaries were active in places like China; (5) With the closing of the American frontier, expansionists looked outward.