They couldn't simply remain at the mercy of the fundamentalists who'd consistently voted against anything that smacked of environmentalism or giveaways to the "loafers" who'd now lost their homes to the sea. Turning from Thoreau and Gandhi and King now to X and Paine and Guevara, they armed themselves and set to righting a horrible wrong.
Crying vengeance for the loss of their great cities and all the history and heritage contained therein, the refugee faction began to wage war on those who'd tried to exterminate them through inaction and then random violence. Realizing they not only couldn't stop them but also had some interests in common, Cannadia opened its borders to what was now called the Restoration Army.
While the rest of the world sought carbon-reduction technology and began to deploy space-based solar radiation shades, North Murrka embroiled itself in a brutal and bloody Second Civil War. The Traditionalist faction, composed of various Armies of God, retained most U.S. military assets and was able to crush the Restorationists. The terrifying war culminated in the seeming fall, and subsequent nuclear destruction, of the now-coastal city of Warshingdon, C.D. - trapping a vast Restorationist force in the city and burning them alive.
Yet the near-complete lack of geographical loyalties allowed the Restorationists to wreck nearly all carbon-burning industries. The massive sabotage campaign imposed on Murrka by force and necessity the same carbon-removal techniques and clean industries that the rest of the world built by choice.
There followed the Theocratic period. Lionizing the old 20th and 21st century televangelists who'd inspired their parents and grandparents, the Traditionalists founded the Res Publica Lyricarum Dei et Libertatis - the Republic of the Songs of God and Liberty. The official Latin title helped bring some reluctant Catholics on board, while most people just used the English name. Religion returned to public schools, atheists and agnostics were banished to ghettoes to fend for themselves, and the success of the Berckeley/Kaltech/MIIT scientists (who'd fled to Suisserland at the first sign of flooding) in refreezing the miles-deep Antarctic ice sheet - was chalked up to God's pleasure at finally having a unified messianic dictatorship on the Murrkan continent.
The vast remnants of the U.S. Navy, not having been able to do much in the war with naval ships and pitiful coastal bases improvised willy-nilly from what they'd been able to salvage before the Flood, merged with the Cannadian rump, ensuring both its continued existence and its gradual cultural merging with the Restorationist cause; or struck out on their own, trading protection and electricity for fuel and food, becoming the Maritime Confederation of Evolu Tanis.
The old mountain states were the first to chafe at the Christian caliphate. Traditionally libertarian, they'd largely sided with the Traditionalists out of caution and respect for property rights. But the treatment of those they still considered their former brothers by the ecclesiastical regime sickened them; after all, was this not a republic of songs of freedom as well as of God? How could oppression of non-believers make them into believers? More importantly, what would happen if the College of Pastors at the Salt Lake ever decided these mountain folk weren't quite in line with the official brand of Christianity?
Thus from their well-defended strongholds, the mountain region declared independence. Some feared yet more bloodshed, but those who remembered the horrors of the Siege of Dinnver managed to convince the government to let them go in peace. After all, the so-called "defectors" were still Christian, were they not? Better to part ways as friends.
As a condition for leaving peacefully, the mountain state called itself a "protectorate" of the Republic, and took the name Sierra Lyricarum as a de jure token of submission in the shadow of de facto complete independence. The Protectorate took in all sorts of scientists and other freethinkers who desperately needed to escape the clutches of the Republic, and became a literal city on a hill. While the Republic retained most military units and installations, the Protectorate held the Callerado Springs Spaceport and other numerically-rare but high-value assets. Their first action was to put tungsten rods in orbit to enable strikes against any target on minutes' notice.
As the northern and coastal parts of the old Unified Societies began to chafe further under the Republic, its government began crackdowns; at first mild, gradually becoming nasty. Once seen by its patriots as a joyous celebration of freedom under God's gentle embrace, the regime became even more like something out of the European Middle Ages, or the worst of the 20/21st century Islamist dictatorships. As the ruling pastors and clerics got more and more paranoid and Puritan, the Republic began to drop its references to freedom and song, eventually becoming simply the Republic of God. The abuses got so bad the Protectorate issued an ultimatum: let any well-defined area secede, or face bombardment of military and political targets from space. As what amounted to the occupied territories of the Republic unraveled from it, they began to try to formulate a theory of government which would keep the dynamism of so-called "free enterprise" capitalism, and combine it with the expertise and state power necessary to avoid godawful catastrophes stemming largely, but not exclusively, from the murder of democracy by oligarchic media.
A syndicalist system was worked out, in which the philosophies of the socialist and anarchist thinkers the old Restorationists had embraced could be put to the test and dynamically compete in a closely overseen free market - a market not under the control of its own largest members, and thus protected from the gross corruptions of simple unchecked capitalism.
As the new polity began to grow in area, wealth, power, and influence, the Republic of God shrunk until it was geographically little different than the historical Confederated States of Murrka, plus some strategically integral western areas (containing ICBMs and the like). Sierra Lyricarum ceased calling itself a protectorate, and openly invited religious and political refugees from the Republic to settle within its borders. By this point the ocean had begun to recede once again, the ice caps regaining much of their lost area and albedo. The founding (or refounding) of Nueva Yorca Ciudad, New Bawstin, and Great Baultimer occasioned rejoicing throughout most of North Murrka; and venomous smoldering outrage in the Republic.
The last straw for the Republic of God was the plan to rebuild Nawleans. Republic propaganda had long listed it as one of the worst pits of sin in all the old world, rivaled only by Hamsterdam, Bhangcook, and Miaami (nevermind how many old Bama codgers could yet be found singing its praises from their younger days). The settlers refused to believe even the Republic would shoot down a civilian seaplane transport in a neutral area; but shoot it down they did, and called it an act of God's righteousness. In a fit of pique the Reverend President threatened to drown the refounded cities in nuclear fire if Sierra Lyricarum didn't renounce them and restore its title of "Protectorate."
In response the Lyricals (now fully comfortable with that name, with its renunciation by the Republic) brought down five tungsten rods on five of the Republic's remaining ICBM silos in its remaining areas of Wyomen and Muntaņa. The threat of additional space strikes put God's Republican Army at its last wit's end. Its commanding general, Buford Wilson, refused all orders to attack Lyrical territory or assets lest his forces be annihilated in minutes from the heavens. The resulting political crisis left the Republic in an inferior position and they sued for a permanent peace. The Treaty of Philladelphya (2180) finalized Lyrical independence, and forbade any economic propagandizing or sabotage by either side against the other - be it Christian capitalist, or the so-called "free enterprise communism" of the fledgling Lyrical economy. Sierra Lyricalia was free.