Dominic Lieven’s Imperial History addresses the popular notion of America-as-empire:
If there is an empire in today’s world, it can only be the US. But whether it is useful to think of the US as an empire is a moot point. Since “empire” nowadays is usually just a term of abuse, the debate can easily turn into a useless trading of insults. It is, however, useful to ask what the history of empire can tell one about the nature and vulnerabilities of US power. Moreover, since the question of American empire is, in fact, being asked on many of the world’s streets and in most of its foreign ministries, there is something to be gained from an historian of past empires tackling this issue. Two points must first be emphasised.
Firstly, empire in the past often prevailed partly because it provided many public goods. It preserved order and peace over vast stretches of the globe. It often facilitated the spread of trade and ideas over long distances. It was usually more pluralist than the modern nation state in its tolerance for multiethnicity and multiculturalism. It was also often associated with the greatest civilisations in history, which could not have flowered without its assistance.
The second point is that empire came in many very different forms. The word “empire” itself has had many meanings even in English, let alone in translation. Some historical empires were much closer to alliance systems than to “states,” in the contemporary understanding of the word. The relationship between an Achaemenid emperor and his regional satraps was nearer to that of George W Bush and the king of Saudi Arabia than that of a US president and the governor of Idaho.
Whether or not it is worthwhile to call the US an empire, it certainly is interesting to ask which particular empires and imperial traditions America resembles. In one sense, the US is closest to the British and the Dutch empires of modern capitalism which created the global capitalist economy. In other respects it is much closer to some of the great land empires of antiquity.