The World Army are an army of human survivors who had survived the destruction by the Old Ones on Earth.
The World Army arrive in groups at Oblivion, Antartica. They are commanded by David Cain, the commanding officer of the US Pole Star.
The day after Matthew Freeman arrives at Oblivion, Commander David Cain orders an attack on the Old Ones' fortress, as they are running low on food.
Scarlett Adams creates a blizzard to hide their arrival. The attack by aircraft missiles supposedly hides their approach and destroys the Old Ones' palace. As soon as Scarlett's blizzard stops, they see that the Old Ones' palace is intact and it was actually an illusion.
The World Army are slaughtered by the soldiers and minions of the Old Ones. When Commander Cain orders a retreat, Matt Freeman causes a chasm in the ice that splits the two armies apart allowing the World Army to retreat to the safety of their camp.
All the countries in the world are represented, according to Richard Cole, hence its name.