Political theory during this time was that if a nation did not expand its borders, it would eventually be taken over. The US had the idea that if they took control of some countries, it would be beneficial to both nations. Also the US believed that by occupying some countries and setting up military bases there, America could better defend itself from the other expanding nations, and protects what we value. The first big expansion was the purchase of Alaska from Russia. Some Americans thought this annexation was a stupid idea, but I think it was spurred by the need of a sort of security barrier. The next huge annexation was that of Hawaii and the Midway islands, which provided advantageous military positioning (Pearl Harbor). The USA also took control of Cuba and the Philippines through military force during the Spanish American war. The occupation of the Philippines gave the US another naval base in Manila and helped to secure American interests in East Asia.
Economically, Pro expansion voices called for trade in new markets, the need of raw materials due to industry, and the protection of our foreign investments. The “Open Door Policy”, which was a positive result from the Boxer Rebellion of China, kept the trade routes open between the US and Asia. Expansion was good for the saturated American market in that the US could export its surplus products. Another Economic plus for America’s