The United States of America: Currently the most powerful Nation in the Northern American Hemisphere, its reach goes from Sea to shining sea, and claims are made to the whole northern landmass (with the exception of the nation of Cascadia). The United States managed to survive by mass evacuation of its northern population and a quick alliance with the Black population in the South after the "Second American Civil War" (1879-1880) which allowed the confiscation and expulsion of traitors out of the country (save for those who hid and reintegrated quickly enough). Needing more land (and food) due to the high amount of people still coming in, the United States embarked in a war of conquest to the South where they took Baja California, Sonora and Chihuahua from Mexico (A war that helped integrate both white and black troops as everyone was just hungry by then).
Politically, the United States still operates as a Republic, with their new capital in Houston, Texas. Most of the political gains done in the 20th century have yet to occur however; Civil Rights for Blacks is something of a given due to having to live with them and due to the destruction of the "Lost Cause" myth after the Second American Civil War. Women's Suffrage, Prohibition, and Presidential terms are something that have never happened, though the first one is starting to get steam.
The United States has managed to make advances in Steam and Electric technology. Trains are the way to travel between the continent, while Electrical trolleys and Steam Cars are used in the cities. Due to the lack of population there's still more houses than apartments in cities, and efforts to reclaim lost territory are still underway. This has led to advanced and experience for the military that has to fight continuously (or be on guard) against predations from the "Neo-Barbarians". Tribes of humans that survived the bitter cold and the fall by adopting a more nomad lifestyle...and a Cannibal diet. The U.S. government tends to subsidize Native American Tribes who survived, or Neo-Barbarian Tribes that accept their authority, with land grants in the frontier to better serve as buffer states.
Domestically, the United States has to deal with Bandits, tribes that managed to sneak by the border, and the political secessionist that plague their most remote possessions and the inner heartland. Some cities in the North (St. Louis, Portland, Chicago, Detroit) managed to survive, and were willing to accept Semi-Independent status in exchange of protection; they agree to pay some money and are mostly left to rule themselves. They are good Trade Hubs for the surviving nations and the many tribes that have formed in the heartland (And are willing to trade). There's still some sectors that feel they should be free to form their own country or City-State, like New York supposedly has, though many who have claimed so can never say who is inhabiting the city.
The greatest danger to the United States, domestically, are "The Knights of the Golden Circle". An organization originally composed of Northerners who sympathized with the South, and now they are a "Fifth Column"-like organization that has integrated into American society whose only goal is the dissolution of the government and the establishment of the "Mythic South" their Great-Great-Great-Grandparents told them about. They have managed to slowly form a web of contacts and even a political party that so far has not gained a single representative in either house of Congress. The fact that it exists however is worrying.
The United States is preparing for the 250th anniversary of its founding, as such reclamation efforts for Washington D.C. have received priority by incumbent President Ted Cruz. Congress however remains deadlocked on whether to remain in its current capital, or return to the previous one once it has been reclaimed.
The current political parties are: The Republican Party, The Constitutional Party, The Green Party, The Syndicalist Party, The Freedom Party, and The Dixie Party (Barely any offices at all).
The Empire of Dai-Nippon: Dai-Nippon (the Empire of the Dragon Throne) is Military Theocracy, with the emperor regarded as "Holy" and descended from the Goddess Amaterasu, and while the military shows respect and submission towards him, it is them who mostly rule the government. Ever since The Fall both were the pillars which kept the country from completely descending into chaos, cutting down freedoms and establishing draconian measures to keep the order. In fact, the Empire could be considered the "Edo Shogunate" with a new coat of paint, but that would ignore many of the advances done; Samurai are no longer the leading class, the army is. Daimyo still exist, but their powers have been curtailed so as to not threaten the emperor's (or the Military's). Serfdom has been abolished, but it remains for the Chinese inhabitants.
The Empire managed to conquer half of China thanks in part to the weakness and opposition to Qing rule which made it ripe for the taking during The Fall. The need for land and food motivated many Chinese to join their ranks while the Empire divided itself into many small states. Many of those now exist in a state of constant warfare, and kept that way by Japan to prevent unification under a single banner. Even so this hasn't stopped the formation of many Nationalist Pro-Chinese organization such as the "Blue Scarves" and the "Dragon Regiment" to name among others. These, and many other domestic dangers are constantly being fought in the shadows by the "Neo-Shinsengumi", the Empire's secret police.
The Empire of Dai-Nippon's military stands as one amongst the most advanced in the world, if only hampered by their sectionalism, grudges, rivalry between the branches and lack of a clear overall strategy. Military prowess is what leads to a greater position, and many thus have an idea of where they can get achievements. Thus, the Empire is in a state of low-key war with the United States of America by the proponents of the "Pacific Front" which only led to the Kingdom of Hawaii to seek protection from the U.S.A. before it being declared a failure until results are shown, the only thing to show being some small colonies in Alaska to fight the American ones. Many consider such posting as a dead end for their career. Of greater prestige (and importance) are the Eastern and Southern front, facing the Andrezi Raj. They have gone to war numerous times in order to conquer and annex said territories and yet, despite some minor gains that can be reversed in the next war, the situation has remained static, with only the conquest of the Philippines serving as a change.
Domestically, the Empire has their hands full fighting against insurrectionists, ranging from the organizations that want to restore Chinese Imperial rule, to those who think the emperor was deceived and wish for him to once more reside in Japan. Nomad tribes and Neo Barbarians roam the border and the interior, with some becoming "Mercenaries" or "Protectors" of villages, paying the tithe to the local Daimyo and basically doing as they please in said village.
The Empire's new capital is in Beijing (still known as Peking in this time). Skirmishes between the Andrezi Raj over Siam are rising, with the conflict threatening to become hot. The current Emperor is Akihito.
The Nation of Deseret: During The Fall and the immigration of citizens to the South, the Mormons decided to stay in their lands and declare themselves independent as the new Nation of Deseret, which would be guided by the Church of Latter-Day Saints, composed of a Council of Prophets, with governmental institutions subordinated to it. While this puts them as a Theocracy in theory, in Practice the Church has little to do with the bureaucratic and political day to day work.
Or so it seems. While the Church does not make its power known overtly, they prefer more subtle ways of "Soft Power" to control the state without being overtly blamed if anything goes wrong.
The Nation of Deseret's military is dedicated more to protecting their territory, and it's limited by their population and their lack of industry. They make up for it by trading with the Nomad Tribes and Neo-Barbarians, as well as with Cascadia, the United States of America, and the independent and Semi-Independent outposts and cities. Domestically there is no dissent, as no one who hasn't embraced Mormonism is allowed to permanently reside within its borders, however their nation has no natural protection in its territory, with enemies coming from all directions they have been forced to employ Nomad tribes as mercenaries to supplement their forces or find those who would cross their borders without them knowing.
The Nation of Deseret claims Utah as their land, and themselves as the "Chosen People" to repopulate America. As such they are in conflict with the United States, though at first the ongoing crisis and the distance between borders made it impossible for said conflict to occur. Trade between both polities was possible at this point, but now with the stabilization of the country, and the shrinking border between them, many are already wondering when will the war begin, or if there's any chance of peace.
Cascadia: The Nation of Cascadia was born from the collapse of Canadian Authority and the rebirth of the Hudson Bay Company. Long having been the De Facto and De Jure rulers of Rupert's Land and Western Canada before the act of 1868, The Fall left it as the only organization with the experience and trust of the surviving people to organize them. Leading an Exodus to their last outpost near Vancouver's Island where they settled, they expanded in time to parts of what is now Oregon and British Columbia.
The ruling body is the Company, with a meritocracy in place so that in order to rise you have to be bureaucratically competent, though a culture of backdoor deals, backstabbing and company politics slowly started to emerge. While the Company makes sure the economy works as intended it does not stop other independent businesses to form, though it does demand they become part of the Company's "Family" paying a flat 10% tax on their profits, thus serving as a Guild of sorts. Though originally a way to make sure products were of sufficient quality, as well as to insure them in case of failure and collapse, it has evolved since.
Cascadia's military lies within the Company's remit. Their soldiers are trained and armed with the latest technology, but are mostly trained in small squad or company tactics, with anything beyond a regiment out of their expertise. Their territories can be easily defended by these tactics, but would be useless in case they find themselves fighting another nation. As such, the Cascadians have managed to form a cordial and profitable relationship with the biggest threats near their borders; the Empire of Dai-Nippon and the United States of America, serving as a mediator in political and trading matters and as the nexus from where both can trade in peace. Needless to say, this has made the Company many a profit.
Cascadians are unique in that they'd rather not employ any Nomads as mercenaries, instead using their own population and tactics. While this has slowed their expansion when it comes to moving inland, it has served them well for their coastal settlements.
The Canadian League/La Ligue du Canada: With The Fall dissolving much of the political authority of the nations closer to the Poles, it was the Independent and self-reliant French-Canadians, or Quebecois, who lead the way into what would become the League of Canada. Moving South to Lake Champlain and settling there among the fisheries. Soon, the small settlement grew with refugees, and other settlements started copying them when they recognized they could survive in areas where there was food and water, places like the many lakes and rivers of the Great Lakes Area.
Not all settlements thrived though, with many dying due to starvation, the extreme climate and raids by Neo-Barbarians. Even the lucky settlements who survived had to resort to more "Extreme" measures in order to do so, with the period being known as a "Shameful dark past", one that many would prefer if it was forgotten.
From the surviving settlements a trading organization soon formed in the first settlement, which soon established French as the Lingua Franca for trading, making it a necessity for all settlements and City-States to learn. Though English still remained, it was French what was slowly taking over and many City-States passed ordinances requiring the teaching of English or its use on Government. Though the settlement grew in power none could become predominant over the other, leading to many conflicts between them. That is until the discovery that the United States was still kicking around, and they had expanded over their territory. The City of Detroit, which had survived thanks to trade with them, gave its allegiance back to the U.S.A. and frightened over the possibility of American take over, they formed themselves into a political alliance while retaining their independence, but agreeing to join together to fight in case any one of them was threatened.
Each City-State has its own military, with their own standards which make it difficult to coordinate when working together. Their decentralized nature however does help them respond to threats quicker. It's helped them keep their territory safe from any predations by Neo-Barbarians, and any Nomad Tribe is welcome in to trade so long as they follow the rules. Their trade can reach up to Cascadia and the United States of America, though with their shrinking borders both know that it's only a matter of time before they clash against each other.
Each City-State has its own political system, though most are democratic, with their own qualifications for voting. Some are more Draconian, while others are more relaxed with their rules. One thing they are all wary of is the chance that another city joins the United States again like Detroit did. As such, any policy that might seem too Pro-American tends to be looked with suspicion.
The Free City of New York: During The Fall the city of New York was one of those who was abandoned, though not all could escape in time. Many died during the evacuation, the hunger, and the extreme weather conditions. As time passed however new inhabitants soon settled in the ruins of what was once one of the most prosperous cities in the Eastern Coast. Tribes of Neo-Barbarians soon took different districts, settling in and becoming merchants of anything and everything. Many disputes are still solved by combat, and the rule of strength is still in effect, with the number of fighting men determining how much territory one holds.
The CSA: After the fiasco that was the Second American Civil War, its leaders and followers managed to escape to Cuba, where they reformed the "Government-in-Exile" of the Confederate States of America...if any would care enough about them that is. They are at best a rump state in Cuba, with enough population to at best occupy half the island, and practice slavery as they wish. So far it was the greater issues that the U.S.A. had to deal with, as well as inertia, that kept them safe. With things changing though, their future is now uncertain.
They receive fiscal and political support from the Knights of the Golden Circle and the Dixie Party, all under the table.