Borders of the United States
The Canada–United States border to the north of the Contiguous United States and to the east of Alaska The Mexico–United States border to the south. The Russia–United States maritime boundary was defined by a disputed agreement covering the Bering Sea, Bering Strait, and Arctic Ocean. The International Date Line essentially acts as the de facto border between the two nations; the USA ratified the USSR–USA Maritime Boundary Agreement, but the USSR failed to ratify it before dissolving, and it was subsequently never ratified by Russia. During the winter, travel between Russia's uninhabited Big Diomede Island and Alaska's Little Diomede Island with a population of 110 is theoretically possible, although not legal, on some occasions when ice flowing through the Bering Strait clogs between the two islands. West of Puerto Rico, the Mona Passage serves as maritime boundary with the Dominican Republic, and the US shares a border with the United Kingdom east of the US Virgin Islands. The Third Border Initiative is an area of foreign policy concerning the Caribbean Sea border between the United States and the Caribbean region.
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