St. John, St. Thomas and St. Croix comprise the US Virgin Islands. These islands of the Caribbean were shared by the US and Dutch up until the US purchased them outright in 1917. The islands are, officially, a US Territory similar to Guam and Puerto Rico.
Oddly, and important to tourists that plan to drive around, it is the only US territory that has left-side driving (just like driving in Britain). Considering the British Virgin Islands are close by, that might not be so odd.