Since I've got today and then a long weekend next week, I thought I'd throw my hat into the ring too. I'm on a post-apocalyptic kick lately, and this one's not going to be an exception.
Having just read Julian Comstock and Fitzpatrick's War back-to-back, this map is going to draw a lot of inspiration from those two books (which are fantastic, by the way).
...and so it came to pass that after the Great Flowering of the Oil Nations, the world descended into the Resource Wars. Much knowledge from that time was lost, perhaps forever. Entire nations were wiped from the map as stronger predators sucked them dry of their natural wealth. Others grew fat and decadent on the spoils. The greatest of these was the American Empire which, at its peak, stretched across most of the two Western Continents. From the verdant farmlands of northern Canada, warmed by a changing biosphere, the Empire fed a war machine which conquered first the feuding and fragmented states of Mexico and the Caribbean, and then pushed into the vast mountains and jungles of South America.
There they bogged down in a decades-long war against their greatest rival, the United Republics of Greater Brazil. Hundreds of thousands of miles of territory were laid waste - the very land and resources the two great powers fought over were destroyed. Eventually, the Empire defeated Brazil, and its constituent republics were carved up by the victor. All of South America worth having belonged to the American Empire. But it was an ultimately futile victory. As the world's environment slid ever further into chaos, great storms ravaged the land and earthquakes reshaped the coastlines. Chaos and death were on the rise.
The Empire, growing brittle and corrupt and facing threats of invasion from the north as Russian TechNom tribes migrated over the melting remnants of the north pole, split into two halves, the East and the West. The East was administered from the ancient city of Philadelphia, while the West was ruled from the new city of Concordia, built on the remnants of three ruined cities just east of the San Francisco Bay, whose rising waters had already engulfed the city of San Fransisco itself and were spreading further.
Many thousands of citizens fled off-world in this time, to the Empire's Lunar and Martian colonies. There they carved out new lives for themselves and passed out of Earth's history forever. In America, the environment was radically changed. No longer did vast fields of wheat and cotton spread across the MidWest and the South; vast, parched deserts had taken their place. The Canadian Breadbasket, unable to fully support both the West and the East, became an endless source of contention. Wars were fought over it for decades, much as the lands of South America had been fought over centuries earlier. By this time, the Eastern Empire was more barbarian than American; a TechNom warlord and his descendants had sat on the throne in Philadelphia for years, and vassal states were falling to revolution, starvation, and plague one by one.
In the year 2412, the last Eastern Emperor, Vassily IV Marco was killed in his palace by a rioting mob, and the East finally fell. The Western Empire was the last stronghold of American culture and power. Ruling from the farmlands of Alaska to the barren ruins of the Baja Peninsula and the Sonora, the West's clone armies and bioengineered plant Sentinels kept its borders safe. The so-called Green Emperors ruled with an iron fist.
But now, some four centuries later, the East is rising again. New, vibrant nations are rising from the ashes of the old Eastern American Empire, and the West faces perhaps the greatest threat it has ever known as the great kingdoms of York, Carolinia, and Jersey unite against them...