Some observers conflate the concept with imperialism; but the US is clear evidence that a hegemon does not have to have a formal empire. Others define hegemony as the ability to set the rules of the international system; but precisely how much influence over this process a hegemon must have, relative to other powers, remains unclear.
这就引出了关于全球霸权比较的另一个问题：对“霸权”真实含义的混淆。一些观察家将霸权列为帝国主义的同义词；但美国是一个明显的例子，说明了霸权并不一定要靠正式的帝国实现。另一些观察家将霸权定义为有能力制定国际制度规则；但霸权必须拥有相对其他列强多多少的影响力仍不明确。