I have not re-written the story overview yet, but it will go something like this...
The war will will span nearly two hundred years and will be know as "the three ages war".
The first is is called the conventional age. This is where the world war began and it ends with the use of nuclear and biological weapons that decimate the earth's population.
The second is the drone age. With diminished populations, the armies of the world begin to rely more and more on unmanned vehicles and AI systems to wage war for them. Eventually, some of this technology becomes self aware and these AI systems establish their own "race" of machines. However, they don't have the ability to manufacture new machines and so they are constantly attacking the tech/toik and savaging them for parts. Because of this, the tech/toik refer to them as "Scavs".
This is what leads to the third and current age, the age of mechs. The armies still face the problem of reduced numbers, but since they must maintain control of their machines, they resort to building larger and larger war machines that can be piloted by a single soldier.
This is the age that the players find themselves in.
Hope that helps it make sense.