Known as the Fourth of July and Independence Day, July 4th has been a federal holiday in the United States since 1941, but the tradition of Independence Day celebrations goes back to the 18th century and the American Revolution (1775-83). In June 1776, representatives of the 13 colonies, then fighting in the revolutionary struggle, agreed on a resolution that at last declared their independence from Great Britain. On July 4th, after the Continental Congress voted in favor of independence, the delegates adopted the Declaration of Independence, a historic document drafted by Thomas Jefferson. From 1776 until the present day, July 4th has been celebrated as the birth of American independence, with typical festivities with fireworks, parades, concerts and also family gatherings and barbecues.
Here is a very interesting video on the Declaration of Independence.