Up until August of 2001, history is precisely as we know it.

On August 10, 2001, what has come to be known as Realmfall occurred. At about 1:30pm in Scandinavia (2:30 in Greece, Finland, and Egypt), reality bent and altered in an instant, in a moment which both the mythos and scientifics described as gut-wrenching and highly disorienting, like a few seconds of being on LSD as the world jumbled and superimposed on itself. The ensuing hours were characterized by mass confusion on every side of the equation. The native mythos (most of them) knew beforehand that their land was to undergo a planar shift, but had been entirely unprepared for the world they joined, with concrete everywhere, abundant metals, towers of steel and stone and glass, roadways to and from every place, and so on. The scientifics were confronted with a reality in which their power cut out, their vehicles couldn't run, all communications were dead, and armies of men and monsters systematically roved the streets to 'claim' scientific humans.
At that time, most of the newly arrived gods did not always transform their victims, and as a result, many people of the affected countries marked in the first few weeks stayed human, even if the god claiming them prefers other races.

In the following weeks, worldwide stock markets crashed as several important economies simply ceased to be, and the Sept11 attack on the United States only exacerbated the decline. The Suez canal was no longer accessible, many low and medium orbit satellites had been knocked dead, the Dardanelles were closed, and many key centres of trade and transit were simply gone to the world economy, to say nothing of the uncertainty and fear that inevitably comes with such a monumental violation of the natural order of things. As word began to spread to the scientific world of what was occurring in these new realms, and word got into the realms that normal areas existed nearby, unaffected by the arrival of the Old Pantheons, the gods deployed their followers to try to contain the exodus of citizens, with limited success. At the same time, militaries, militias, and desperate bands of individuals attempted to strike into the new realms to wrest back control from the old gods. Any mass incursion inevitably met with failure.

Similarly, attempts organized by the gods to venture out into the scientific world to take control of governments there met with immediate and spectacular annihilation, as modern firearms and explosives tore the primitive armies to pieces. It seemed a stalemate, modern armies couldn't last long inside, primitive armies couldn't last long outside. Attempts to do any more than infiltrate ceased as both sides managed their respective and massive hurdles. The scientific world simply contained the problem at every border, and rapidly assigned every relevant scientist to learning what needed to be known about the nature of these realms, while they dealt with the massive economic and supply hurdles that would define the decade after realmfall. On the inside, things were no less dire, as gods scrambled to solidify their positions against one another. In the first several years, control of food was key. Gods able to create and distribute food effectively achieved an early advantage, and became early targets for those with a more militaristic bent.

Even as the realms remained embroiled in frequent civil wars, some gods began to look outwards, beginning to understand the scientific realm. Hephaestus and Wepwawet made especially concerted efforts to conduct large-scale trade through the borders. Hephaestus in particular was able to capitalize on divine alchemy, creating rare earth metals for trade to great advantage, until the other gods picked up the same knack, and the global market was flooded with the "rare" metals, collapsing the price of every one of them and adding to the economic woes of the outside world.