The United States comprises fifty constituent states and one district. Located in the North American continent, the country gained independence from the rule of Great Britain in 1776. At that time, it had only 13 states. Between the 19th and 20th century, the United States expanded across the North American continent by including 37 new states and acquiring a number of overseas territories. Washington, D.C. is the capital, and New York is the largest city. The Postal Service of United States mainly uses the abbreviations of American states. They help to process the mail quickly with the help of automated equipment, such as OCR (Optical Character Recognition). These two-letter, no-period, state abbreviations -- recommended by the U.S. Postal Service -- should always be used where a ZIP code follows. They can also be used in any context where abbreviations are appropriate. Take a look at the states, their postal abbreviations, their capitals, and the largest city in each state. Unincorporated territory is a legal term used in the United States law. It connotes an area controlled by the government of the United States. However, this area is not a part of the United States proper. These territories were created to govern newly acquired land while the borders were still evolving. Currently, American Samoa, Guam, United States Virgin Islands, and ten other territories are under the US possession. However, the other ten are uninhabited. The Federated States of Micronesia (FSM), the Republic of the Marshall Islands (RMI), and the Republic of Palau are the associated states of the United States. These states are sovereign in nature, but have entered into a Compact of Free Association (COFA). This Compact was renewed in 2004 for a period of 20 years. Commonwealth, in the context of insular areas, is an organized but unincorporated dependent territory of the United States. Currently, the Northern Mariana Islands and Puerto Rico are the two United States insular areas classified with the status of commonwealth. The District of Columbia is the only federal district of USA. Washington was a separate municipality within this district until 1871. Later, an Act of Congress was passed to merge the district and the city into an entity. That is how the city of Washington came to be known as Washington, D.C., where DC stands for District of Columbia. When one state invades the territory of another state with the intention of holding the territory at least temporarily, it is called military occupation. This invasion occurs without the volition of the actual sovereignty of the occupied country. Here is a list of postal abbreviations of Military States of the United States of America.