Short answers, pulled from the story.
On the 2nd of January 1776, a Continental Army aide named Stephen Moylan wrote a letter to Joseph Reed using the phrase United States of America for the first documented time. This phrase defined a nation and declared intent to seek powers from the United States of America to Spain for assistance in the Revolutionary War.
The first inhabitants of North America migrated from Siberia approximately 15,000 years ago, crossing the Bering land bridge or following the now-submerged Ice Age coastline into the heart of the continent. Small, isolated groups of hunter-gatherers moved alongside herds of large herbivores, establishing ice-free corridors along the Pacific coast and valleys of North America.
The Declaration of Independence was adopted by the Second Continental Congress on the 4th of July 1776. Thomas Jefferson wrote United States of America in a rough draft of the document two days after the Congress passed the Lee Resolution to create an independent, sovereign nation.
The United States is a federal republic of 50 states and a federal capital district, Washington, D.C. The U.S. asserts sovereignty over five unincorporated territories and several uninhabited island possessions, including American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands.
The United States entered World War II in December 1941 after Japan's attack on Pearl Harbor. The country had begun supplying war materiel to the Allies of World War II in March 1941 while remaining initially neutral.
The 48 contiguous states and the District of Columbia have a combined area of 3,796,742 square miles. The United States is the world's third-largest country by total area behind Russia and Canada.