Events of "X-Men: First Class" take place. 30 year old Lehnsherr and 30 year old Xavier meet for the first time, and will form an antagonistic best friend relationship. The CIA forms Division X, which includes Professor X (Xavier), Magneto (Lehnsherr), and Mystique (Darkholme). James Howlett tells Xavier and Lehnsherr to fuck off. Magneto kills Sebastian Shaw. Mutants prevent World War III. Xavier is injured and wheelchair-bound. Magneto forms the Brotherhood of Mutants. Cuban Missile Crisis takes place.
Note: Xavier lies to Logan in the first X-Men movie, stating that he met Erik when he was 17. They were in fact both 30, Xavier possibly lying to add emphasis to the longevity of their friendship.