[nine_k]

Empires stay empires in the original sense only when there is a core where people are privileged, and colonies where people are exploited and lack rights. Roman Empire stayed like that for a long time (even Latin rights were introduced relatively late), Russian Empire had a lot of that, and British Empire was practically an epitome of that.

I don't see how the modern US is comparable: equality is formally enshrined in the Constitution, and whatever inequality exists is delineated more by ethnic / cultural lines than by geography of birth or living, driven by private xenophobia, not institutions.

[andrepd]

The USA have extreme amounts of influence all over the globe. They have performed countless invasions and over 100 regime-changes in the past century.

The power relations in global capitalism between the US and its tributaries is not dissimilar to the relations between e.g. Rome and its provinces. Hence calling America an empire.

[analyst74]

US has done much better than previous empires.

Despite starting off with genocide of natives and slavery, it slowly improved over time in terms of addressing internal strife, which is probably a major contributor to its longevity as a global power.

[inglor_cz]

For a big power, the US is relatively young. As a country, it has been around for 250 years, but as a world power, mere 100. That is on the young side when compared to other historic empires.

The Roman empire in the 1st century AD looked remarkably stable and rich. You wouldn't be able to prophesize the crisis of the 3rd century from the status quo in Hadrian's times.

[nine_k]

Which post-medieval states had a much longer tenure as a comparable world power? Spain kept for about two centuries, and Britain maybe for somehow more. Can't readily tell about China, but it did dominate its vicinity both culturally, economically, and militarily for quite some time, before a long and miserable decline that lasted until late 20th century.

[inglor_cz]

France, the UK, Spain, Portugal, the Ottoman Empire, Russia, I would say. All clocked at 250+.

Of course, we may split a lot of hairs discussing what "comparable" means. Certainly all of those were great powers, controlling distant shores and distant nations for long generations.