On December 16th:

 1653  Oliver Cromwell Becomes Lord Protector of England

On this day in 1653, Oliver Cromwell, a key figure in the English Civil War, assumed the title of Lord Protector of the Commonwealth of England, Scotland, and Ireland, effectively becoming the head of state.

 1773  The Boston Tea Party Takes Place

A revolutionary act unfolded on December 16th, 1773, when American colonists, protesting against British taxation, boarded ships in Boston Harbor and dumped chests of tea into the water in what became known as the Boston Tea Party.

 1944  The Battle of the Bulge Begins

One of the largest battles of World War II, the Battle of the Bulge, commenced on December 16th, 1944. It was a major German offensive on the Western Front and a pivotal moment in the conflict.