Why is the American military's presence in Hawaii important?

The United States has maintained a series of military installations on the Hawaiian Islands because the country has long considered itself "a Pacific nation." Once Americans settled the long western coast of the U.S. portion of the North American continent, they began to look across the Pacific Ocean, both for economic and security reasons. The Pacific, like the Atlantic, is an enormous expanse of water that both connects continents and provides a form of sustenance in its natural resources. As the United States grew as a nation, both geographically and economically, its ability to secure its western coastline while forging economic ties with Asia grew in importance. The Hawaiian Islands, situated at the midway point between Asia and North America, with their natural deep-water ports and agricultural potential, became a strategic asset, prompting the construction of sizable military installations there, particularly the large naval base at Pearl Harbor and, as air power grew in importance, Hickam Air Force Base. 

The importance of U.S. naval facilities in Hawaii were apparent not only to American officials, but to military planners in Imperial Japan as well. The December 7, 1941 surprise attack on U.S. military installations on the islands was intended to radically-degrade the American capabilities to project military power across the ocean. Japan sought to colonize Southeast Asia, as well as China and the Korean Peninsula, and eliminating, even if only for a few years, America's ability to project military power to Asia was central to its planning. 

With the end of World War II and the emergence of the Soviet Union as a potential military threat--Russia also has a long coastline along the Pacific Ocean, and maintains a sizable Pacific Fleet within its navy--the military bases on Hawaii remained extremely important. U.S. aircraft carriers and ballistic missile and attack submarines all operate out of the naval bases on Hawaii, and played a major role in protecting U.S. access to important maritime trade routes, protecting U.S. allies like Japan and the Philippines, and defending against Soviet (and, today, Russian) naval forces and long-range bombers, which are increasingly patrolling closer and closer to American shores, just as was the case during the Cold War. 

Economically, protection of maritime trade routes across the Pacific is essential to the United States. Asia is, collectively, vitally important to the U.S. economy. The overwhelming bulk of trade in goods takes place via maritime cargo traffic. Large container ships sail back-and-forth across the Pacific everyday, and any threat to a disruption in that traffic is considered a very serious issue. The U.S. Navy plays the major role in protecting that movement of ships, and the growth of Chinese naval capabilities, along with a resurgence in Russian naval activities, means the importance of the military bases in Hawaii will not end anytime soon.