The post-apocalypse setting of Rifts Earth turns on an event called "The Coming of the Rifts", written in the rulebook to occur in 2098 at the fall of a so-called "Golden Age". After a military skirmish in South America, there was a nuclear exchange that occurred at a magically-auspicious moment and the massive death--acting as a ritual sacrifice--opened the world-wide network of magical ley lines; the resulting energies wrecked Civilization and brought the end of the Golden Age about.
Okay, first thing first: change the date. The setting works far, far better if we set the Coming to occur on December 21st, 2012. This change allows us to easily exploit all of the readily-available material regarding various fringe authors, etc. writing books and making videoes about UFO, the occult and all that stuff. If you really want to get that specific--and there is not much benefit for doing so--pick one of the various occult conspiracies/paradigms and use the local time of the relevant location of power wherein the Rifts erupt.
Now, after that, you get the usual ruined world-Dark Age-fragile recovery scenario. In North America, this covered a combined period of about 300 years (as of Year 101 of the Post-Apocalypse calendar). In the start date of the original rulebook, it is P.A. 101 and the Coalition States are starting to invade Minnesota. Those three centuries make for a lot of time, time in which survivors can again not only recover to the old world's previous apex but eclipse it and go further; in our real history, this is the fact of European history between Rome's fall and the emergence of the Middle Ages- by the time of the Italian Renaissance, post-Western Rome had easily caught up to Rome's remnant in the east (Byzantium) and began eclipsing it.
I say that, due to many of the world's major states having Continuity of Government plans in place for a cataclysmic event, the recovery phase of technological survivors can be accelerated--can be, because those survivors can fail due to external attack or internal collapse--significantly. It is this accelerated recovery that I say is what allows the Coalition States (as well as Triax/New German Republic and other such states in the setting) to not only recover as fast as they do, but to pass the former apex and move into new areas of advancement and deployment.
Now, the other big change that comes is that magic and other supernatural forces aren't so weak as to be immaterial most of the time anymore. They're obvious, and they're so wide-spread as to be omni-present in certain places. In North America, this includes my home town of Minneapolis and St. Paul--nexus of 100 ley lines--as it becomes the Magical Kingdom of Tolkeen. (Yes, I will post my own take on this, and it's going to make the most of this ridiculous name.) Making use of existing real world conspiracy theory regarding Continuity of Government, we can say that many parts of the world do not escape the Coming and get scoured by the energies bursting forth from the Rifts. This is what allows many of the magic-based states to establish themselves; the Coming wiped clean the sites, killed most of the people and warped the rest, and the new magic-active sites arise from a combination of native survivors (acclimated to supernatural power) and magic-using/magic-native aliens moving in to colonize the ruins.
Next time, we'll talk about the baseline rules for magic and the supernatural, and then transition into the Coalition because without this background many of the posts about the Coalition won't seem to be much more than misery porn. Good setting work does not do that, so we're laying our foundation accordingly.