On January 20th:

 1265  The First English Parliament is Formally Convened by Simon de Montfort

On January 20th, 1265, Simon de Montfort convened the first English Parliament, a significant step toward the development of representative government in England.

 1936  King George V of the United Kingdom Passes Away

A pivotal moment in British history occurred on January 20th, 1936, with the passing of King George V. His death marked the end of an era and the beginning of the reign of King Edward VIII.

1981  Iran Hostage Crisis Ends as 52 American Hostages are Released

A chapter in international diplomacy concluded on January 20th, 1981, as the Iran Hostage Crisis ended with the release of 52 American hostages after 444 days of captivity.