After a ton of confusion surrounding the Galactic Readiness system in Mass Effect 3, BioWare has decided to step in and elaborate on how it factors into the Mass Effect 3‘s ending.

Those who have chosen to disregard the game’s multiplayer might find that no matter how many War Assets they might obtain throughout the game, the Galactic Readiness stays firmly at 50% — BioWare assures gamers that this does not affect the ending, however, and that the Effective Military Strength bar is what really matters in the end. The multiplayer acts as an alternative to gathering War Assets in the single-player mode. Essentially it boils down to this: Effective Military Strength will determine the game’s ending and can be filled through War Assets or multiplayer — how to chose to prepare for war is up to you.

Source: BioWare