In no significant order time wise or importance:
- Invasion of Italy: Removed Italy from the game. Hastened German take over of Italy as well.
- D-Day: Do you need an explanation of this? If so I will edit.
- Stalingrad: Also really famous so I would hope no explanation is not necessary.
- Kursk: Largest armored battle in all history. Was a series of battles that had over 3 million men involved. Russians had more casualties in this one battle then the US had in the ENTIRE war.
- Battle of Britain: The Failure to Invade or to force the surrender by bombardment and air combat allowed Britain to hobble on till the USSR was invaded and the US joined the war.
- Battle for the Atlantic: The failure to halt the supplies coming in from the US allowed Britain to chug along and the USSR to continue fighting Germany.
- Pearl Harbor: Its a Pacific issue but its action resulted in Germany declaring war on the US, not the other way around.
- African Campaigns: Secured Oil and required Germany to get creative with artificial oil production.
I would argue 3,4,5,6, and 7 where pivotal turning points for the Axis powers.
1 and 2 where big deals none the less that affected the war.
It's really hard to argue for or against certain things being major events, but these where super big deals.