It has been proven time and again throughout history that in order to survive, a nation must expand its borders and become more powerful. This is shown by the European countries' power at the beginning of the 20th century. They were the strongest countries in the world, and between them they controlled almost the entire globe. Soon after, America also became imperialistic. Three reasons America became imperialistic was to acquire naval bases and refueling stations for their ships, to control new markets in which to sell American products, and to get more raw materials and resources to help feed the growing American industries.
The first reason Americans turned imperialistic was to control naval bases at sea in order to strengthen their military power outside of their boundaries. In 1885, America's navy was described as a "fleet of washtubs", and their army wasn't much better. It was obvious that if America wanted to protect its interests in foreign countries, it would need a stronger military force. The first step was to be able to defend itself should any foreign countries encroach on its territory. Naval bases were the key to this. So, after the Civil War, America looked to the Pacific islands of Midway, Samoa, and Guam, among others, to serve as bases and refueling stations for their navy. All three of these islands held very strategic positions. Midway was in the more northern Pacific Ocean, Samoa protected the southern Pacific, and Guam was the closest pacific island to the Philippines and China. .
Another reason America became imperialistic was to get more raw materials and resources. Like any industrial nation at the time, America was pumping out their manufactured products faster than the raw materials could keep up with. In order to keep producing at the rate it was, America needed to find another source from which to acquire their raw materials. An example is West Africa, where America used its Open Door Policy to freely trade.