On June 7, 1776, Richard Henry Lee, a delegate to the Continental Congress from Virginia, moved a resolution for independence.
For the year leading up to Lee's resolution, members of the Congress (and people throughout the colonies) were somewhat divided over whether to officially and formally separate from Great Britain. Britain's ruthless prosecution of the war against the colonial uprising (which included the hiring of mercenary troops) and the publication of Common Sense had resulted in a decisive sea change of popular opinion. More colonists were calling for independence -- a permanent break from Britain.
On July 2, Lee's motion for independence was approved. John Adams predicted that July 2 would be celebrated as America's Independence Day. But....it was not to be.
Two days after voting for independence, the Continental Congress received a document that formally articulated the reasons for independence, including their grievances against Great Britain. This document, known as the "Declaration of Independence," was authored by Thomas Jefferson and was approved on July 4, 1776. And it was that day (July 4) that subsequent generations of Americans have chosen to remember as their nation's birthday.