some AH scenarios to ponder

(1) In the 1960's the Civil Rights black movement starts. USA Federal Government shows no interest in it, or suppresses it and arrests its ringleaders, etc. The Begroes see no peaceful recourse left, and resort to guerrilla warfare. Continue as Vietnam, but transferred to the southeast of the USA; sabotage and explosions; police and KKK convoys blown up on road landmines, etc. It drags on for years despite all the white man's trumpetings that they will suppress it quickly; white state control in affected areas is reduced to main roads by daylight. Compare the real Irish War of Independence in the 1920's. The USA space program is at a halt because supplies can't be transported safely to Cape Canaveral across guerrilla-infested areas.

(2) Unlike in the real world, in Europe (and not only in central and south America) a species of tree or bush makes sap that dries out to make good rubber. Europeans can waterproof clothes etc much easier and develops effective diving equipment much sooner than in reality.

(3) The Ottoman and Seljuk etc Turks convert from their old pagan religion to Christianity instead of to Islam when they invaded Anatolia.

(4) Indonesian sailors find and settle Australia many centuries before Europeans get there,

(5) Varro does not lose the Roman XI XII and XIII'th legions in the Teutoburgerwald, and Rome Romanises all the Germans up the Elbe, and then up to the Oder. That leaves many fewer barbarians to invade the western Roman Empire later.

(6) Yellow fever gets from Africa to southeast Asia.

(7) The tsetse fly, and the livestock-killing "nagana pest" disease which it carries, gets into the Middle East in old times.

(8) The Byzantine Empire manages ro keep Islam's forces out of Africa, or the Crusaders manage to overthrow the Muslim rule in
Egypt. Egypt remains Coptic Christian.

1 A real nightmare scenario. Could have happened, and lasted decades if not generations.
2 Evolution of different species while keeping homo sapiens is ASB to me, but granting it would make at least a small area of technology get a boost. Also do a number on Latin America's economy, with probably negative side effects.
3 A more Christian and less Moslem world. Maybe the Moslems would be even more desperate and violent. Or maybe the Turks would develop a different "flavor" of Christianity for Christiandom to fight over. I am sure we would find a way to make a mess of things.
4 Probably the Indonesians and Aboriginies would develop a mixed culture, since early Indonesia would not be as "overwhelming" as later Europe. Maybe it would be better able to withstand the eventual Europeans.
5 Rome lasts longer, although it would probably get even more decadent and fall eventually. With even more decrepit an empire, the aftermath could be even darker.
6 Chinese civilization gets screwed, probably finally recovers in an unpredictable form.
7 All civilization gets screwed, with a probably longer recovery time needed...if ever.
8 Much like 3, only centered in Egypt instead of Turkey.