Going back on my previous comment, I think one ITTL historian might refer to the period of Drew's TL (1972-1990s) as, like, one giant period of global crisis.
Maybe calling it the Late 20th Century Crisis, or the Late 20th Century Tumult, unifying the various horrors the world has experienced into one vast period of chaos.
Here are the various conflicts that have occurred:
* The energy crises of the 1970s, and the Second Great Depression.
* The Agnew Presidency, the political polarization of the period, the rise of Donald Rumsfeld, the succession of several American states, the war in Cuba, the creation of the CSA, and the nuclear Second American Civil War (which is I think will be the central catastrophe of the Late 20th Century Crisis).
* The rise of Pinochet, Operation Condor, and the brief border war between Argentina and Brazil
* The Brazilian dictatorship, and Brazil's civil war.
* The Greece-Turkey-Cyprus conflict, and Greece's civil war.
* The Southern African conflict, South Africa's descent into a genocidal white supremacist state, the environmental damage to Southern Africa, and the coming South African civil conflict.
* The brutal Indo-Pakistani War, and India's slow breakup and collapse into civil war.
* The Sino-Mongolian War, the rise of the Lesser Mao, the China White epidemic, the Chinese democide, the Kwangsi Nuclear Disaster, China's collapse into another warring states' period, the rise of the Chinese caliphate, and the border conflicts between the various powers over China's territory.
* The various skirmishes in Indochina throughout the 1970s.
* The Troubles of Northern Ireland.
* The near breakup of Canada after the almost-secession of Quebec.
* The collapse of many Arab states, including Saudi Arabia, into fanatic and radical Islamist regimes, the increasingly land-hungry Iraq, the increasingly expansionist and racist Israel, the political chaos of Iran.
* The overthrow of Estado Novo, and its replacement with a more radical communist regime.
* The political transition of the Spanish state, and the separation of the Basque region.
* Zaire's annexation of the Central African Republic.'
The late 20th century will match the period between 1914-1945 as a period of general violence and death.
In world history terms, I can imagine a massive contrast is going to be made by future historians between what people imagined the 20th century would be like, and the bloody, apocalyptic reality it turned into.
It will be seen as one of the great tragedies of history. People at the turn of the century, full of all of the optimism of the Belle Époque, imagined a future of unparalleled prosperity and world harmony, where technology would herald abundance, would eliminate poverty, and through interconnection, would bring the nations of the world together. The result was a century that saw two world wars, widespread genocide, nuclear devastation, economic turmoil, Fascism, Stalinism, the horrific collapse of China, brutal civil wars in India and Brazil, the chaos of decolonisation (I can imagine the war in South Africa being lumped into this period) and finally the apocalyptic religious fanaticism of the Christian States of America.
The chief lesson from the period, I imagine, would be to never take anything for granted. People in OTL still question how a nation like Germany could have gone down the horrific path of Nazism. This sort of confusion would increase exponentially in TTL, certainly I think with regard to the collapse of the United States. For decades, if not centuries to come, people will struggle to understand how a nation that basically conceived of the idea of checks and balances, that prided itself as a haven for political refugees, that saw itself as the global arsenal of democracy and which fought a global war against authoritarianism only decades beforehand, was able to succumb to the very thing that it was set up to oppose. Above all, historians might point to the fact that long-cherished concepts like "liberty", "freedom" and "democracy" were bandied about and trivialised by political authoritarians until they had become worthless buzzwords, and before Americans could realise it, their political system had failed, their constitution had been torn to shreds, and the country collapsed. Certainly a keen awareness of the political system, of the duties of citizenship, and of civic responsibility will become absolutely paramount to education in the future, if anything like catastrophe of the 20th century is to be avoided.
Following on from this (and I think it has been mentioned before on this thread), the second lesson from this entire period would probably be the dangers of zealotry, of any kind. Any ideology, taken to its radical conclusion, will be seen as potentially lethal. As a result, historians might end up calling the entire century "the Age of Fanaticism" or "the Age of Ideology", hopefully, in the minds of historians, that a future world order will be built around consensus and reflection.