In 1979, the world changed forever. On October 23, 1979, a malfunction in the Soviet Union's early warning systems resulted in a limited nuclear exchange between the United States and her NATO allies and the USSR and her allies in the Warsaw Pact. While "limited" in nature and not species-destroying, the widespread destruction and chaos that followed changed the world forever. Many major cities across the globe, including New York, Moscow, London, Paris, Berlin, Vienna, Istanbul, and Beijing were hit by nuclear weapons. The nature of the mistaken war, later dubbed the "Hot War" despite it not being an official war, allowed for a much more limited exchange as the remaining Soviet and American governments scrambled to stop the violence. This likely saved the Earth, though radically changed all the countries within.
What followed the Hot War was little better than the war itself. A nuclear winter, combined with crop devastation from the nuclear-plastered American Midwest and Soviet farmlands (where many missile silos had been hit), left many in the world to starve or barely subsist on what food remained. During this period many governments existed only in theory or as little more than warlords with Constitutions. Even the American government largely consisted of whatever federal officials were left, party be damned. During this period many old grudges were taken out and borders shifted mightily. The Middle East saw a resumption of the Israeli-Arab Wars (which Arab states, starved of resources, eventually lost) as well as limited Iran-Iraq War that resulted in the Revolutionary Iranian government capturing the majority Shia areas of Iraq and Saudi Arabia. India pressed Pakistan until it gave up Kashmir, South African apartheid fell apart into a bloody civil war, and even the United States did not survive the transition whole. California, Nevada, Oregon, and Washington State joined together into a self-proclaimed "Pacific States of America" due to their feeling of isolation and being taken for granted by the rest of the United States. Under unlikely favorite President Ronald Reagan, the Pacific States of America successfully seceded and have existed ever since as its own state within the United Nations.
The United States and Soviet Union themselves were not long for the world, either. The two states managed to come together in 1982 in Hong Kong (a state very much in transition from British ownership to God-only-knows-what) to sign an accord officially ending the "war". The Hong Kong Accord would later be expanded to form a new world government to succeed where the UN had failed. Called the United Earth Government, it would be a governing body based out of an independent Hong Kong (after annexing Macau) that would seek to better govern and control world interests ahead of those of any single country. To encourage this, exclusive councils were done away with in favor of those made up of rotating countries. The UEG would also have unilateral control of human space activity, and every member country would be required to donate certain numbers of military assets so that the UEG would always be a force to be reckoned with. While seen as more extreme than the more-or-less defunct United Nations, the gamble succeeded following the official beginning of the UEG in 1991, and it continues to the current day of 2119. Though its only territory on Earth is Greater Hong Kong, the UEG has control over many space elevators, orbital stations, interplanetary outposts, and space colonies both in habitats and on other planetary bodies. Its navy in outer space is certainly something to be reckoned with.
In the fallout of nations, two new post-Westphalian meganations came into being: the United Nations and the World Soviet. The United Nations really only shares the name of its predecessor when it was formed in 1993-6 in response to the formation of the World Soviet. Instead it is a union of many states across the world who value social democracy, capitalism, and cultural independence. The nations that make it up are many, and are part of the UN for different reasons. NATO more or less became the outright militant wing of the UN, gaining new members in the aftermath of the Hot War in Eastern Europe. Nations in Southeast Asia joined to escape the Communists who had consumed Indochina, while those in Africa joined as the Sahara continued to advance and they felt themselves limited in options between destruction and UN membership. There is no true single leader of the United Nations, though the North American Republic (a union of Canada and what remained of the United States formed in 2001 with a new Constitution) tends to lead the charge, and the state is headquartered in Geneva. Life in the UN is one of being environmentally and culturally conscious while living most of one's life likely officially unemployed but surviving due to a universal income provided by the UN government. Most citizens live in various megacities while land around them has been reclaimed and spend their time working human industries such as art, literature, the erotic arts, and politics. AI is practically a natural part of the UN and a common sight everywhere, from the military to the supermarket to the bedroom. Those seeking excitement tend to join the military or journey the offworld colonies, a chance to begin again in a glorious land of opportunity and adventure.
The other primary nation in the world is the World Soviet, a union that began in 1989 and was finalized in 1991 between China, the USSR, Vietnam, Cambodia, and Laos joined together as a single nation to recover from the Hot War and become a more united group of Communists. In reality, it was a power grab by China who cared little for grabbing the Warsaw Pact (though China-friendly Albania was able to join) and wanted instead to be a major driver in the force of Communism in the next century. China certainly succeeded and continues to be the dominant force of the World Soviet in 2119, especially as the New Ice Age continues to claim land in the former USSR. Headed from the sprawling capital of Astana, the World Soviet is a largely compact state besides its few other members in Albania, Ethiopia, and Mozambique, and has gone long ways towards creating a single World Communist culture and ideology by mixing various identities and philosophies of communism into one, creatively dubbed World Communism. World Communism is highly statist, proletariat-driven, economically-concentrated, and human-centered in philosophy and life in the World Soviet reflects that. Life is as communal as possible with families as we understand them barely recognizable in favor of communal living within the massive megacities that dot the landscape. Brand new cities founded as the New Ice Age advanced greatly reflect this in their utilitarian design that resembles from afar massive industrial factories. They are far from lifeless, however, and instead are abundant with the workers who drive them through raw human strength and power; the World Soviet is very suspicious of AI and generally uses only "dumb" machines with as much human influence as possible. This results in far more hard work for Soviet citizens, who look down on the lazy and decadent Westerners in the UN who spend all day in luxury. Not to say the World Soviet doesn't have culture--far from it, Soviet culture is at its peak now that it is shown more and more within the UN and independent nations and consumed all over the world and offworld--but that the average Soviet citizen is more concerned with family and friends and work life than UN citizens are with their endless artistic pursuits.
The other major faction of the world, though not so nearly united, is the League of Independent Nations. Formed originally by India, Indonesia, and Iran, the organization has grown in order to become a third path for many nations all over the world. Eschewing a single ideology, the nations of the LIN tend to be very diverse in population and political opinions and only seek companionship in order to remain separate from either the United Nations or World Soviet. While life highly varies within the nations, it tends to be one of personal independence, mixed with machines, and highly-focused on environmental concerns. India is certainly the leader in that aspect, as it has single-handedly grown itself into a superpower that has set its unique philosophies and ideas to a higher place on the world stage. Their current goal is to continue joining the disparate nations of the world together, particularly the independent nations of Africa, and eventually be able to directly challenge either meganation up front rather than having to rely on playing both off each other. This will be helped by the rising power of Indonesia and by Iran and Brazil having money poured into them by India to rise as world powers on their own. If one wants more adventure in regular life, country living, and diverse religions and philosophies one does not need to look further than the LIN.
The world itself is, as always, highly mixed. While living standards tend to be rather high compared to our own, it did not come without a cost. In 2119 the world population is just around where it was in OTL's 2000. A New Ice Age began after a period of global cooling brought on by the Nuclear Winter of 1979-1984, and has consumed much of the world's north. This has lowered global temperatures and exasperated climate problems around the world. While there have been benefits in some areas, particularly arid areas in the Americas, Middle East, and Central Asia, it has had catastrophic results elsewhere. Even Europe has been forced to adapt heavily to the conditions and much of Russia was consumed by ice and snow. Some continue to live in these wastes, but most fled south. While world poverty is not really what we know in our world, world riches are not very well known either; most of the world lives somewhere in the middle. However, not all is bad. World peace has been maintained for the most part besides a few independence movements/war and regional conflicts like the Congo War (1999-2004), largely due to the influence of the United Earth Government. Humanity has moved far into space as well, colonizing virtually every planet and planetoid possible in the Solar System. In addition, many humans live on orbital habitats or habitats in the asteroid belt made from hollowed-out asteroids. It is hoped one day humans will live more offworld than on, and the first attempts at colonization of Proxima Centauri are underway. Overall it is a mixed world of choked megacities teeming with life and serene, rebuilt countryside ready to be renewed. It is a time of moving forward and upward, and of creating a new existence for humanity far removed from what once was.