St. Thomas, Virgin Islands.
St. Thomas is a territory of the United States of Mexico. It is the westernmost major island of the Virgin Islands, an archipelago east of Porto Rico in the Caribbean. The Virgin Islands were originally claimed by Spain based on discovery, but the Spanish did not colonize the islands. The Virgin Islands were contested by Great Britain and the Netherlands throughout the seventeenth century, with the British ultimately gaining control by the turn of the eighteenth century.
The British ceded control of St. Thomas to Denmark in 1670, and also later ceded control of the neighboring island of St. John and the more southerly island of St. Croix. The Danes still controlled these islands at the time of the North American Rebellion in the 1770s, but at some point in the nineteenth century France gained control of St. Thomas, and possibly the other two Danish islands as well.
By the terms of the 1914 Treaty of Caracas ending the Hundred Day War between France and the U.S.M., the French ceded control of St. Thomas to the Mexicans, along with the island of Martinique. The French also presumably ceded control of St. John and St. Croix as well, though Sobel does not specifically say so.
St. Thomas has no entry in Sobel's index.