The official name of the United States is the United States of America. According to some people, the name America came from the shortening of the official name.
The newly discovered lands were given the name 'The Americas'. The United States used the name of the continent to refer to its new country.
Before The USA got its name, America, the name was used for south America by the Spaniards. The Spaniards then gave up the name, as they wanted to name the new lands after Columbus. Shortly, the name was used to refer to America the country.
According to one theory, the name emerged as the British called the ones who left to live on the new continent 'the Americans', as the continent was called America. See also how the united states was formed.
According to one theory, when people landed on the new land they were encouraged by the US government to call themselves Americans so that they achieve a unique identity and differentiate themselves from the British people.
When the United States declared independence in 1776, the name 'The United States of America' was formally introduced, and as a result, the term Americans started to be used to describe inhabitants of the country.
According to one theory, the fact that the United States became the first independent country in the new continent, America, helped it get that name first.
When colonists landed in the new land they were called colonists. After the US independence, it became necessary to find another name to describe the US citizens.