This has been a common comparison of empires and western powers since the fall of the Western Roman Empire. In Western history, the idea of Rome has become one of legitimacy, those states which embody it, embody the legitimacy and power that Rome projected. The Holy Roman Empire was named as such to display a connection with Rome and its power, along with the power of the Catholic Church. The British Empire is often compared to the Roman Empire and now, with the United States as the leading power in the World, it is likened to Rome. The similarities are similar in that Roman culture and society are foundational to western culture; however they belie a fast depth in the comparison. The issue is the attempt to compare an ancient power to a modern one. Under closer scrutiny the comparison fails as the social, economic, and political structures of these societies do not correspond. The comparisons are made between the IDEA of Rome and the modern political realities, how modern individuals attempt to mold Rome into a modern understanding, which cannot work, there is simply too much difference.

Compared in order:

Holy Roman Empire:

  Voltaire's joke about the H.R.E. is that it was neither, Holy, Roman, nor an Empire; while blunt, they are in effect true. Holiness is the most accurate part as the empire early as it was sanctioned by the Catholic Church until it was further shattered by the reformation and rendered even more impotent. The Empire itself was not an empire as the tern generally implies a sense of expansionism, however the H.R.E did not expand a great deal and while lead by an emperor, he was elected by the aristocracy of the empire. In almost every sense, the H.R.E. was the antithesis of the French state under Louis XIII and XVI, with the aristocracy defeating the centralizing authority of the King/emperor. By the age of Napoleon, the empire had become a completely outmoded, archaic, feudal patchwork with little collective power. The empire itself was hailed as the inheritor of the Roman state; however it held few similarities to the original in politics with the elective nature of succession feeding the feudal nature of the power schema.

The British Empire:

 The British Empire was ruled by a King who held power by dint of Parliament. This holds some similarity to the Roman imperial court; however this is only in appearance, as the Roman emperor ruled as the head of the armies of Rome rather than by aristocratic allowance. The Senate could apply pressure to the emperor, however he was beholden to his success militarily and his popularity to the people of Rome. The British Empire was also primarily maritime, gaining vast sums of money through trade goods and taxation, while the economy of the Roman Empire was pre-modern, with the main sources of wealth coming from conquest. There was a significant amount of trade within the Roman Empire but also a huge amount of wealth drained from the empire in exchange for luxury goods from the Far East. The attempt to compare these states, and in reality any modern state, fails under closer inspection as the social, economic, and governing concepts diminish the comparison.

The United States:

 The United States holds superficial similarities to the Roman Empire however only very superficially. The Roman Republic was not a democracy, the Empire was definitely not a democracy, the economy of the United States compared to that of Rome holds no compatibility, the social mobility holds little resemblance. The concepts which appear to fit is the heavy current of nostalgia in the Unites States, where we were better an less corrupted in the past. This is very present in the Late Republic and Early imperial Rome as the idea of decadence leading to the moral and military decay of Rome was one put forward by both Pliny the Elder and Younger (amoung many others). The idea of moralism in the United States is strong as it was in Rome, however you cannot compare the moral systems of Rome to that of the United States, a post-enlightenment and Christian influenced state. 

The United States can be compared to the idea of Rome as they both filled somewhat similar roles in their time, however an effective and useful comparison between the two cannot be truthfully made without making massive presumptions and overlooking culture, society, governance, and economic. Despite this, the power of the time will always be compared to Rome as it has remained the benchmark of a superpower in Western society.