I do not believe any individual leader or country would now be able to create an empire of subjugated states by means of force - far too much transparency, and far too much interconnectedness for that to happen.
There may be a more subtle change though; a cultural shift in values. In the late 1800s, it was GB that had the honour of being that dominant cultural exporter ( and also the dominant territorial power). In the late 1900s, that switched to the US, and has been with them for some time - but China are now a serious contender.
And you cannot discount the rise of religious fundamentalism - the spread of Islam, Sharia Law, the desire for a caliphate and all that, but again I doubt they will achieve that aim.
Any cultural dominance or empire building will be through economic trading blocks, I think.