Best shot IMO is a Soviet Union that makes more noise about the whole internationalist stateless thing (without actually practicing what it preaches, of course, but still). No Stalin and no or a different WW2 would likely be required for this. China and India are taken over by Communist regimes (China somewhat like OTL, India perhaps as a result of Britain trying to hold on for longer and radicalising opposition) and the USSR officially absorbs both countries into one unit covering most of Asia and, with similar absorption policies in Eastern Europe, half of Europe--in practice this super-USSR is a dysfunctional mess, but at least on paper it is indeed "one country containing more than half the world's population".