Mass Effect 3: Galaxy at War system is a new way for players to manage and experience the galactic war from multiple fronts, including a new 4-player co-op mode (4:25)
The key to saving the galaxy is the "Galactic Readiness" level, measured by Commander Shepard's ability to apply every possible asset -- people, weapons, resources, armies, fleets -- in the final battle against the Reapers. Players can impact their game's Galactic Readiness level in multiple ways via the Mass Effect 3: Galaxy at War system, including multiplayer. Other platforms and interfaces will be announced in the coming months. It is important to note that the system is entirely optional and just another way players can have control over their game experience -- it is still possible to achieve the optimal, complete ending of the game in Mass Effect 3 through single-player alone.