The Declaration of Independence, written in 1776, contains at the very top of the document the phrase "The unanimous Declaration of the thirteen United States of America" (capitalization as in original). So it wasn't "added"; it's been there since the very beginning. There are other countries who are known as the local equivalent of "United States of (whatever)" (one example is Mexico, which is officially "Estados Unidos Mexicanos"), but "the United States" is almost universally assumed to refer to the United States of America.
admitted
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Territories
The Letters in the word U.S.A meanU-UnitedS-StatesA-of America
This is called the Western Hemisphere.
The root word of "unhappy" is "happy." The prefix "un-" is added to "happy" to create the opposite meaning.
an affix that is added in front of a word while a suffix is an affix added at the end of a word
McKinley added Puerto Rico the the US as a reulst of the Spanish -American War. The Philippines and Cuba were also added temporarily. Roosevelt added the Panama Canal Zone, also temporarily.
The prefix that can be added to the word "integrate" is "dis-", resulting in the word "disintegrate."
To my knowledge, the proper capitalization is The United States of America. However, when using the letters only, it is the US or the USA.
The prefix that can be added to the word "destructive" is "non-."
A suffix is added at the end of a word. A prefix is added at the beginning.