Is it at all possible that a country could conquer the whole world through simple imperialism? I don't mean with an ideology like Communism but with just plain European imperialism.
The easiest way I can think of is to have a freak accident or massive social unrest take down one of the major powers such as the British or Russian empires in order to allow one power to reign supreme.
To keep things relevant to the age of imperialism, no PoD before 1700.
well the Hapsburg approach went quite well. Dont conquer marry, and persuade the Pope to give you a large part of the rest of the world. Possibly there might just have been an outside chance of a world empire if Charles V had not divided the Austrian and Spainish Hapsburg territories and the riches of the new world had been better used.