<P> Armed conflict began in 1775 . In 1776 , the Second Continental Congress declared a new , independent nation : the United States of America . Led by General George Washington , it won the Revolutionary War with large support from France . The peace treaty of 1783 gave the new nation the land east of the Mississippi River ( except Canada and Florida ) . The Articles of Confederation established a central government , but it was ineffectual at providing stability , as it could not collect taxes and had no executive officer . A convention in 1787 wrote a new Constitution that was adopted in 1789 . In 1791 , a Bill of Rights was added to guarantee inalienable rights . With Washington as the first president and Alexander Hamilton his chief adviser , a strong central government was created . Purchase of the Louisiana Territory from France in 1803 doubled the size of the United States . A second and final war with Britain was fought in 1812 , which solidified national pride . </P>
when did the united states became a nation
1776