I don't think it's possible without creating global institutions that empower a world government to have serious leverage against rebellious countries. What would be best is an already empowered United Nations equivalent, which by the force of powerful members can give crippling sanctions against people who threaten the world order. This alt-UN would also have serious moral authority, able to stop genocide and civil war and bring down the worst of tyrants (Nazi Germany, 90s Yugoslavia, 90s Rwanda, etc.) by direct intervention if needed.
If we get into future technology, the future of this organisation might be placing all of the world's oceans (outside of the continental shelf of nations) and space under its control. If space-based solar power is the future (it could be), and the only ways to access space are sea launches (especially the floating launch loop proposed by Keith Lofstrom, which Lofstrom suggests can double as an energy grid linking the world, a power loop) and an orbital ring (once you have enough launches), then the alt-UN can assert control over that too. This is similar to a "hydraulic empire"--with control over the majority of the energy grid, a substantial standing army, all space colonies, and all space resources (which with an orbital ring can outcompete most Earth-based resources), then the alt-UN can bend all Earth nations to its will. This could evolve toward a system where each nation was little more than a state (not necessarily a US state, but maybe more of the Spanish model) within a Federal Republic of Earth.
The United States would be a cornerstone in this organisation, no doubt, given the vast industrial and agricultural capability of the US and its large population. The rest is a matter of finding the right allies in Europe and Asia to create some common framework, and also creating adaptibility so wars over decolonisation don't utterly destroy the organisation. Such an organisation could be the wet dream of imperialism where "enlightened" Europeans and Americans with some Asians (Japan, probably) rule over and brutally exploit most of Africa, Latin America, and Asia, or one which evolves toward more equality where nations share their wealth and resources for the sake of improving the world, or anything in-between.