On December 7th:

 1787  Delaware Becomes the First State to Ratify the U.S. Constitution

On this monumental day in 1787, Delaware became the first state to ratify the United States Constitution, contributing to the formation of the fledgling nation.

 1941  The Attack on Pearl Harbor

December 7th, 1941, is a date that lives in infamy, as the Imperial Japanese Navy launched a surprise attack on the U.S. naval base at Pearl Harbor, Hawaii. This event propelled the United States into World War II.

 1972  Apollo 17 Launches, Marking the Final Apollo Moon Mission

The Apollo 17 mission, the final crewed mission to the Moon, launched on December 7th, 1972. Astronauts Eugene Cernan and Harrison Schmitt explored the lunar surface, leaving a lasting legacy in space exploration.