Payback War

The Payback War was a clash between the Whitebeard Pirates (under Marco) and the Blackbeard Pirates about a year before the current storyline.

Details
The Whitebeard Pirates sought revenge for the betrayal of Blackbeard and the resulting deaths of Whitebeard and Ace during the Battle of Marineford.

Aftermath
According to Robin, Marco was utterly defeated. Nekomamushi mentioned that the Whitebeard Pirates commanders have disappeared since then.

Teach's victory lead to him being considered one of the Yonko.

Luffy, who was training on Rusukaina for the two years on roughly both sides of the War, was unaware of its happening.