For the new recruits, the last president died during the unprovoked Illuminate attack on Super Earth.
"The President died heroically, defending the Presidential Security bunker with only a pistol against waves of Illuminate foes."
Source: HD2 xTwitter
The game was released on xBox and a new warbond with a Halo ODST theme was released.
They also announced an upcoming warbond and a huge addition to the game that will be implemented in September, which might also get some people playing again to warm up for the new content even if they don't care about the Halo warbond.