Basically a half to a full dozen larger towns (>10,000 people) and one or two mid-sized cities (>100,000) on the eastern side and double that on the Western side of the Mississippi survive to become the nuclei of survivor governments. Larger cities survive only because the bombs were duds or missed entirely. Eugene OR, Pocatello ID, Johnson City TN, and Valdosta GA are among the leading cities to survive initially though half or more will fall to thugs, riots, radiation, and starvation.
Half the population dies in the strike. Half of the survivors die of starvation, internecine violence, and disease over the next 6-8 weeks. Half of *those* survivors are dead by the end of the first year. By New Year 1985 things stabilize at 10-12.5% prewar population, about 25-30 million people with most being in Oregon, Idaho, western Texas, central and eastern Kentucky, southern West Virginia and the tip of Virginia, northern Tennessee, southern GA, eastern NC, and Maine. Other pockets may exist too. Expect the first decade to be harsh, infant mortality looks like it did two centuries earlier and trained doctors are more valuable than everything but water and food. Electricity is a memory for almost all survivors and hygiene is abysmal. Feudalism emerges in many areas while barter trade becomes the norm. Scavenging is dangerous but common, especially for metal and machine parts, while walled city-states of less than 5000 become semi-common. Children are apprenticed, formal educational systems may exist in a few places but by and large are a memory. Population will start to increase as soon as food allows and will see a generational spurt probably beginning about 1995 or so.
By the end of the century a few dozen Larger 'nations' emerge that will coalesce into 3 to 6 definitive nations by 2015. Technology remains a hodge-podge of World War 2, American Civil War, and even Revolutionary War levels for another generation. In the interim, governments remain largely reluctant to centralize at first but a few authoritative ones do so and trigger a larger war. Everyone agrees not to use nuclear weapons, it is the common thread that allows for negotiations of a continental trade union by 2025. At least one nation that emerges is fascist, one socialist, but most are variants or carbon copies of the good old USA.
Europe is a nuclear wasteland that becomes a reminder of the folly of man and warfare. Switzerland survives as does Austria minus Vienna, this Helvetian Republic eventually grows to include Bavaria, Trento, Bescanson, Granche-Comte, Baden-Wurtemberg, and Savoy. The rest of Europe is a graveyard with a few dozen policies of note, the largest is the Scandinavian Union out of Trondheim that is fiercely isolationist but will trade readily. By 2015 it is the second most powerful nation in former Europe with a resurgent Albania not far behind. The bulk of NATO countries are trying to coordinate some sort of European Union but to date can only agree that they want nothing to do with West or East ever again!
South America is where the powerhouses of Argentina, Brazil, and Chile (now with Peru and Bolivia) reside. They have formed the Trimuvirate Pact that coordinates technology transfers, research, and infrastructure together with a military alliance and free trade zone. Embraer has begun producing it's own jet aircraft and Brazil's air force is the strongest in the world. Triumvirate Pact members now include all of the continent save Venezuela and Colombia (which are observers along with Cuba) as well as Panama, Costa Rica, and Trinidad/Tobago.
Mexico is a power but got hit by EMP backlash rendering much of the northern half of the country unusable for industry until the machinery for making electricity could be replaced. Upon doing so it recovered quickly and made forays into the bordering US states, unchallenged until the Greater Texas Directorate began reprisals of the bloodiest kind. Even today tension remains.
South Africa is a powerhouse flirting with implosion after it's apartheid policies were disbanded barely three years after the war. Civil war had chafed much of the country and JoBerg was already lost. With both sides fearing what else might be lost a federation of three governments came to be: a Zulu state in the east, an Afrikaan state in the north, and a Union state in the West. They play nice because they fear what a true all-out war will do to themselves and the Union state plays referee with the other two. In the interim, Botswana, Namibia, Mozambique, Lesotho, Zimbabwe, Malawi, Madagascar, Angola (both sides of the Civil War surprisingly willing to make peace after the bombs fell) , and Swaziland have joined as 'partner states' (satellites) to build more railways and highways to further develop the internal ecomomy. Synthetic fuel plants were already built here and are being expanded to make the Union of Southern African States a top diesel/petroleum exporter and a top 5 industrial power. Along with Australia, New Zealand, and IndoThai (Indochina, Burma, Thailand, Assam state, and Bangledesh merged for fear of annhilation from a desperate China) it is one of the Big four powers that counter the Triumvirate and police the 'Old World'.
China is a living nightmare consumed by civil war, starvation, and a return to 17th century technology levels. While the Korea's are all but a memory and Japan's condition unknown (none who go there return though overhead high-altituse reconaissance flights indicated *electric* lights visible at night before recording a radar signature and target lock before turning around at high speed). Eventually a Pentax of governments emerge, the remnants of the old Communist government in Manchuria and the central coast opposed by the Canton Confederation, Xiu Empire, Tibet, and Uighuristan. Yunnan is an indeoendent state considering a union with IndoThai within the year.
India and Pakistan survived thebwar in excellent shape with a chance to lead the world as two big powers. Sadly the War of 1989 proved both were nuclear powers and the Union of South Asian States struggles to rebuild as well as clean everything up around a 300 mile radius of the Indus River. Its economy is only beginning to show the signs of dynamism hoped for in 1990 and it will remain a second tier power as a result.
Australia lost Sydney, Darwin, and Pine Ridge but miraculously the missiles intended for Melbourne fell short and the one that landed in Brisbane was a dud! They are still exactly where they fell and no one cares disturb them. Australia has emerged quickly as a world leader along with New Zealand which survived the war intact. A strict non-nuclear policy is in place but standards of living here are among the highest in the world with Wollagong as one of the top universities in the world now (alongside UNAM, University of Sao Paulo, Federal University of Rio de Janiero, Federico Santa Maria Technical University, Indian Institute of Technology, and University of the Witwatersrand).