For much of U.S. history, the vast oceans separating America from Europe and Asia protected the nation against attack by foreign enemies. Today, those oceans are as much a hindrance as an advantage. America's military has repeatedly been called upon to defeat overseas adversaries, and getting to the fight has been a huge logistical challenge.
With only a fraction of its military machine deployed forward, planners must have a way of surging troops and equipment to distant war zones in time to avert defeat. America's enemies typically fight close to home, while U.S. forces must transport everything they need over thousands of miles.