Though too few people have responded to this thread, this is a serious issue. If the French had granted full political rights to the Muslims in Algeria, it's quite likely that the Tricolore would still to this day fly over Algiers. If they'd done that during WWI, they'd had had up to a million more men of military age to conscript, and their sacrifice might well have made those changes stick. Senegal is another French colony that could have remained in the French Union, as their contribution on the Western Front was quite significant. The Senegalais were considered as elite troops, and they often spearheaded French offensives along with Morrocan forces. These two are also places where French rule was well implanted. IIRC, the first president of Senegal was a member of the Académie Française...
As for Britain, I see no reason why a little more investment in Newfoundland, butterflying away the lost of Dominion status in 1934, wouldn't keep them in the British camp. Elsewhere, I see them being able to keep control of East Africa, the CAF, and Ceylon with some policy corrections. If they and the French can pull out the Suez mission without Isreali involvement and make it stick, I'd imagine that the Trucial States, Oman, and Aden would also probably remain under the British umbrella for security reason if nothing else.
As for Portugal, if Salazar comes to power, you'd need him to be more flexible on colonial policy to placate the independance movements in the colonies, a Portuguese Union so to speak. That seems a stretch, though, given how little capital Portugal could provide for colonial development.
The Dutch might have held onto Suriname and Irian Jaya, but that would have been more out of coincidence than concerted effort. By the 19th century the Dutch weren't in the colonial expansion business anymore, except for consolidating their hold on the DEI.
Belgium has no hope whatsoever of holding onto the Congo, so they're out at the beginning. It's a fluke of history, IMHO, that they even have any colonial territory.
Spain doesn't have any colonies by 1900 that are even worth holding on to, so even if they keep them, so what?
Anyway, there's my two-cents. Being that they're American, they're worth even less than they would have a few years ago!
