Just because I'm feeling particularly evil, I'm wondering if it would be possible to get the entire planet under the control of one central government. It doesn't have to be direct control--there can be vassal states--but there does have to be worldwide hegemony. Since the obvious PODs are the early ones, such as Rome lasting til present day and just conquering everyone, there's bonus points for having as late a POD as possible. GO!
Edit: Just to clarify, you need to say more than just (as an example) 'The British Empire conquers the world, since they were the biggest!' Why would the British have the motivation to do this? How did they overcome the alliance of nations that would obviously rise up against them? These are questions that are implied in the challenge.