On July 4, 1776,  the Declaration of Independence from the Great Britain.

However,  the actual independence happened two days earlier.

Source: History.com

Therefore,  4th of July is considered as "birthday" of American and independence day. 

Declaration of Independence wasn't signed on 4th of July.  It was signed on Aug. 2 . 

Source: National Archives

Fourth of July celebrations became after the War of 1812.

By the 1870s, Fourth of July celebration became the most important holiday on the calendar in the USA

Independence Day, New Year’s Day, Christmas Day and Thanksgiving Day were declared as holidays in 1870. First four designated federal holidays by the Congress.

According to the Congressional Research Service

Fireworks in Fourth of July celebrations is a symbol of national pride and patriotism since first Independence day in 1777.