The volcanic and coral island in the Pacific Ocean is roughly the size of Chicago. Guam, popular with Japanese and South Korean tourists, has a population of about 163,000. It is about 3,500 kilometers southeast of North Korea, much closer than it is to the United States.

The closest US territory to this remote island is Hawaii, which is almost 6,500 kilometers away. Its proximity to China, Japan, the Philippines and the Korean Peninsula has long made the island a vital post for the US military.

Read more: Which US cities could North Korea's ballistic missile hit?

United States territory in the Pacific

Guam became a US territory in 1898 during the Spanish-American War. Japan seized it for more than two years during the Second World War. In 1950, Guam was recognized as an 'unincorporated organized' territory of the United States by an act of Congress.

The island has limited self-government with an elected governor, small legislature, and non-voting delegates in the US lower house, the House of Representatives. 

Its status as a US territory adds to its strategic importance for the US, which can beef up its military presence there without seeking any clearance, as it's required to do when building up defense installations at its bases in countries such as Japan and South Korea.

'Tip of the Spear'

Since the Second World War, when the American troops reclaimed the island from the Japanese, Guam has remained a strategic outpost for the US military. Dubbed the 'tip of the spear' by the military, it is home to a naval base and Coast Guard station and an Air Force base that saw heavy use during the Vietnam War. The military bases cover about a third of the island.

Guam is protected by the advanced US Terminal High Altitude Area Defense (THAAD) anti-missile system. About 6,000 US marines are stationed in Guam, and there are plans to send thousands more.

ap/ng (AP, Reuters)