Which of the 3 would be best described as an imperial nationalist?
- USSR voluntarily disbanded. Moskow currently can't even assert military dominance over the Ukraine. Sole claim to global relevancy for Moscow is the soviet era nuclear arsenal.
- China might practically be able to invade a small island off their coastline, but it isn't obvious that they could tolerate the backlash. The quality of their army is largely unknown because they haven't used it seriously in decades.
- US has flattened multiple Middle Eastern countries in the last few decades, the world meets in New York to conduct diplomacy regardless and barely makes an issue of this. Has had a comparable number of soldiers stationed in Germany to the German army (at least it did recently, I think that changed under either Trump or Biden). The US dollar is used for international trade and the people who move off it get invaded for unrelated reasons. Technically they did voluntarily shrink their empire too though, because of that business with the Phillipines, but they are still the undisputed military hegemon and set the pace of global affairs. By far the most invasive worldwide spy network.
Now this may well be a good state of affairs but the parliamentary democracy is not the timid and delicate flower in this picture. It is the most imperialist of the 3, by far. I can speak in sweeping generalisations because this is a big, obvious and hard to miss state of affairs.
Democracies are just more effective than dictators at building and maintaining an empire.