The US, China, India, and Russia are all superstates. China maybe isn't since 90% of its population identifies as Han, so it can be viewed as the nation-state of a very large ethnic group, but we're still talking about a huge population and dominion over widespread areas belonging to other groups.
In addition to those, I can almost see a unified Latin (or Spanish) America, coming from midcentury communist revolutions espousing pan-Latinism, and maybe a more federal and less intergovernmental EU. But the latter is less likely in alt history than in the future. Even at the peak of pan-Europeanism, when George W. Bush provided a plausible common rival for all major political movements in the European core, France and the Netherlands voted against the EU constitution.
EDIT: the reason I interpret China and India as in control of a continent is that I mentally break down the world into more than 6 inhabited continents. To me, if Europe counts as a continent, then so must the major constituents of Asia, i.e. South Asia, Southeast Asia, East Asia, the Middle East, and north/Central Asia. Under these definitions, India and China both control large majorities of their respective regions in terms of both population and land area.