That's... really difficult.
You're not going to avoid decolonization. The colonial empires cost money, and as the developed world transitioned from industrial capitalism to post-industrial capitalism, their worth would have all but vanished. Late-19c Europe needed colonies to export manufactured goods to; present-day Europe mostly trades with itself.
In a few places, you can get one state where there are several. Beedok already mentioned the East African Federation, and you already mention India; I'll add Indochina under Vietnamese domination, the Malaysia-Singapore merger, and some of French West Africa. Maybe a Polynesian confederation? But that won't get you below 100.
Mergers of preexisting countries are possible... but really hard. A pan-Latin American communist state could exist, if you contrived your TL toward one. Eurofederalism is really hard - tellingly, a lot of EU countries were tepid about supranationalism even when things were going well, right before the recession started.
You're not going to avoid decolonization. The colonial empires cost money, and as the developed world transitioned from industrial capitalism to post-industrial capitalism, their worth would have all but vanished. Late-19c Europe needed colonies to export manufactured goods to; present-day Europe mostly trades with itself.
In a few places, you can get one state where there are several. Beedok already mentioned the East African Federation, and you already mention India; I'll add Indochina under Vietnamese domination, the Malaysia-Singapore merger, and some of French West Africa. Maybe a Polynesian confederation? But that won't get you below 100.
Mergers of preexisting countries are possible... but really hard. A pan-Latin American communist state could exist, if you contrived your TL toward one. Eurofederalism is really hard - tellingly, a lot of EU countries were tepid about supranationalism even when things were going well, right before the recession started.