Here is the real explanation:
Originally--after discovery by the Columbus expedition and further exploration by European explorers, the continents known today as North and South America, were called various names, "Columbia" being popular as many people naturally thought the territory should be named after Columbus.
Meanwhile a rather unknown explorer, Amerigo Vespucci, born in Florence in 1454, sailed with Alonso de Ojeda in 1499, parting with him even before land was sighted in the West Indies. Vespucci, sailing in his own ship, then discovered and explored the mouth of the Amazon, subsequently sailing along the northern shores of South America. He returned to Spain and entered the service of the Portugese and then back to Spanish service where he eventually was made pilot major. Vespucci not only explored unknown territory he also invented a system of computing exact longitude and arrived at a figure computing the earth's equatorial circumference only 50 miles short of the correct measurement.
Vespucci wrote many letters about his voyages including one to Lorenzo de' Medici in which he described "the New World". Several of these letters were rewritten and sensationalized by an unknown author, who published these forgeries as "Four Voyages" in 1507. Of of these forged letters was read by the brilliant young German cartographer, Martin Waldseemuller, who was so impressed with the account that he include a map of the New World in an appendix to his book Cosmographia Introductio, boldly labeling the land "America."
Waldseemuller's map roughly represented South America. When later cartographers added North America the name was kept. Later the great geographer, Gerhardus Mercator, gave the name "America" to all of the Western Hemisphere.
The major reason Columbia did not catch on is because Columbus to his dying day refused to acknowledge that the new land was in fact a previously "undiscovered" country and insisted that the lands were a part of Asia. Spain continued to call the lands Columbia until the 18th Century.
The name "United States of America" was chosen by the colonists to show their unity as independently established colonists into a cohesive federal government against the British monarchy.
During the 18th Century "America" came to be used as a term of endearment to the millions of immigrants seeking a better way of life. Believe me when they spoke of going to "America" for a chance at the brass ring they were not thinking Mexico, Brazil or even Canada!
I believe that out of this era arose the common use of shortening the USA to just America and the strong identity of the name with the US.
Incidently, the Vikings or Norsemen were the first Western European explorers of the Western Hemisphere, mostly notably Leif Ericsson who called the land, "Vinland" for the abundant wild grapes that they found on the East Coast, but since he didn't have a good publicist the name never caught on.
It is also likely that Eastern Asian or Russian fishermen had made contact with the Aleutian Islands and there are settlements in Alaska that predate Columbus.
Not too mention the multitude of "native american" tribes that had long since existed on the North and South American continent while Europe was just a baby. These peoples have various names for the land in their own language.
Getting back to today--get over your envy.
"North America" is Mexico, US and Canada. "South America" from Columbia to Argentina. "Central America" from Belize to Panama.
But just plain "America" is only the USA.
--Eduardo
