What significant event does July 4th commemorate in the United States?

July 4th commemorates the adoption of the Declaration of Independence, a pivotal moment in American history. On this date in 1776, representatives from the thirteen American colonies formally declared their independence from British rule. The Declaration, primarily authored by Thomas Jefferson, outlines the colonies' grievances against King George III and articulates the principles of individual rights and government by consent of the governed. This moment marks the beginning of the United States as a sovereign nation, celebrated each year as Independence Day to honor the values of freedom and democracy that the Declaration embodies.

The other options touch on important historical events but do not relate specifically to July 4th. For instance, the signing of the Constitution occurred later, in 1787, and the end of the Civil War took place in 1865. The start of the Revolutionary War is generally associated with events such as the Battles of Lexington and Concord in 1775, which precede the adoption of the Declaration. Hence, the correct answer highlights a foundational moment that fundamentally shaped the nation.