‘Fortress America’ Is Getting Smaller and Smaller

Donald Trump has a knack for raising big strategic questions. The US president is massing military power in the Caribbean; he’s reportedly on the verge of approving a military strategy that deprioritizes far-off regions. In doing so, Trump is reviving a debate with deep roots in history: Where should America draw its forward line of defense?

The nation’s military responsibilities expanded steadily across North America in the 19th century. The US also drew a protective buffer around the Western Hemisphere with the Monroe Doctrine. By the late 19th century, Washington had grabbed the outworks of that hemisphere — Hawaii, Samoa, Puerto Rico — to secure its oceanic approaches. In the 20th century, it enlarged that perimeter farther still.