An alternate timeline by Althistorian 2005.
What if the Sino-Soviet border conflict in 1969 erupted into full-scale nuclear war?
March: The Sino-Soviet border conflict begins with Chinese attacks on Zhenbao/Damansky Island. Chinese forces occupy the island following the Battle of Zhenbao Island.
August: 3 border incidents occur in the western Chinese province of Sinkiang. The conflict finally escalates into full-scale war following the third incident at Tielieketi, on August 13, 1969.
September: Cuba and the Warsaw Pact join the Soviet side of the war. Chinese nuclear missiles are not able to reach that far at the moment, but as the PLA advances into Soviet Central and Eastern Siberia, they bring their missiles with them. The Soviet Red Army advances into Sinkiang, prompting the Indians to invade Tibet, taking advantage of the opportunity. North Korea joins the war on the Chinese side, but US president Richard Nixon persuades South Korea not to join on the Soviet side, fearful of the nuclear annihilation of his Korean ally.
October: The PLA advances west, further into Soviet Siberia, but the Red Army halts them. With a stalemate, or even a Soviet counterattack, supposedly approaching, the Chinese nuclear arsenal is hastily launched at important Soviet cities like Leningrad and Moscow, and also at the advancing Red Army. Soviet warheads are then launched at important Chinese cities like Shanghai and Beijing in retaliation, as well as Pyongyang, the capital of North Korea, killing North Korean leader Kim il-sung, as well as his son, Kim jong-il. However, Chinese leader Mao Zedong and Soviet premier Leonid Brezhnev narrowly escape death in their private bunkers while millions die in the nuclear fireballs that now engulf most of their cities.
November: Natural winter combines with nuclear winter to create, in China and the USSR, the coldest temperatures ever recorded in the entire world. In November alone, millions of people freeze to death due to the shabby conditions of what little housing has survived the nuclear bombings. Millions more die from radiation poisoning from the previous month's nuclear attacks in what is now the most devastating war in all of human history. The United Nations agrees unanimously to expel the USSR, with Germany replacing the USSR by a popular vote. China is not expelled from the UN because they aren't even in the UN; the Chinese seat continues to be held by Taiwan, which has declared neutrality despite their long-standing rivalry with China.
December: India leaves the war, not having declared war in the first place, reestablishing Tibet as an independent Indian protectorate. The Indian seizure of Tibet goes completely unnoticed by the Chinese government, and the UN also ignores it. Meanwhile, the communist Eastern European member governments of the Warsaw Pact are finally overthrown by their citizens, who launch a massive revolution due to the lack of the Soviet Red Army to oppose them. Free elections are held, and Eastern Europe is finally freed from communism after 20 years. Alexander Dubček, the Czechoslovak leader who initiated the Prague Spring a year before, finally returns as the leader of Czechoslovakia, which ends up becoming the most progressive of all the former Warsaw Pact countries, finally splitting up peacefully into Czechia and Slovakia.
1970: With the nuclear dust settling all over Eurasia, South Korea decides to reunify Korea and encounters little resistance from the crumbling, leaderless North Korean army. In a few months, the UN agrees that the war is over, but also that no countries should attempt to enter Soviet Russia or Communist China to inspect the situation. Korea is officially reunified and admitted to the UN the following year. The Cold War is also declared to be over, despite the Vietnam War and other Cold War conflicts still continuing, but President Nixon promises to end them as peacefully and as soon as possible, guaranteeing himself a full second term due to this overshadowing Watergate, which never becomes a scandal in this timeline.
1972: The Vietnam War is ended diplomatically, and free elections are held across Vietnam. American aid is also provided to Vietnam to help clean up the damage from the war.
1973: A revolution occurs in Iran, but not one led by Ayatollah Khomeini as in OTL. It is actually a CIA-sponsored coup that installs a Shah allowing for more freedom, which causes the people to realise that Ayatollah Khomeini, the Islamic imam they had admired all these years, is actually preaching less freedom than even the old Shah. But with the new Shah in charge, the people of Iran have great hope for the future. Meanwhile, the Yom Kippur War happens between Israel and its neighbors, during which American support of Israel causes Arab states to close off oil trade, triggering a recession which outlasts the war.
1973-6: With the Cold War over, the CIA stops funding authoritarian Latin American￼ dictatorships, causing a wave of democratic revolution to sweep over the region. American military spending is also cut massively, allowing the US government to finally have a budget surplus. However, President Nixon agrees with Congress not to lower military spending too much, so that the US military is still the most powerful in the world.
1976: After winning the Republican primaries against incumbent vice president Gerald R. Ford, California governor Ronald Reagan wins the presidency against Democratic candidate Jimmy Carter due to the Watergate scandal not happening and the end of the Cold War ensuring the political dominance of the Republican Party for at least the next decade or two.
1977: Following Nixon's post-Cold War policy of ending support for anti-communist pseudo-fascist dictatorships, President Reagan decides to depose all remaining dictatorships, starting with Iraq, which is led by the Ba'ath Party and its de facto leader, Saddam Hussein.￼
1980: President Reagan is reelected following the successful deposition and replacement of numerous dictatorships, and continues this policy to the end of his term.
1984: Incumbent vice president George H.W. Bush succeeds Reagan as president.
1986: The UN decides to work towards a complete world peace, as well as the end of poverty and other societal issues, with a deadline-ish goal set for the year 2000.
1988: President Bush is reelected.
1992: Following a mild recession caused by slight mismanagement of the economy, Democrat Bill Clinton is elected president, defeating Republican candidate Pat Buchanan.￼
1996: President Clinton is reelected.
1998: An alleged affair with a White House intern completely demolishes President Clinton's reputation and credibility, but that doesn't stop the 2000 election from being determined by a very close Florida recount as in OTL.
2000: George W. Bush, son of former President George H. W. Bush, is narrowly elected president.
2003: The UN finally decides to declare world peace, limiting military budgets across the globe to purely defensive spending.
￼2004: President Bush is reelected in yet another narrow election, but not as narrow as in 2000, due to the UN's successful declaration of world peace the previous year.
2008: African-American Democrat senator Barack Obama is elected president.
2012: President Obama is reelected.
2016: Billionaire real estate mogul and TV personality Donald Trump is elected president as the Republican candidate, despite all the jokes about him being a madman.
2019: President Trump is impeached.