The first war associated with the Declaration of Independence was the American Revolutionary War. It had already begun in 1775, and the Declaration was adopted on July 4, 1776 during that conflict.

Quick context

  • The war began with fighting at Lexington and Concord on April 19, 1775.
  • The Declaration of Independence was adopted more than a year later, on July 4, 1776.
  • So the Declaration did not start the war; it declared independence in the middle of it.

In one line

If you mean the first war around that moment in U.S. history, it was the American Revolutionary War.