HomerSimpson: I'm pretty confident that those totals would both beat the US given it's relatively short history compared to the other two.
Are you sure ? I'd say that the USA were involved in many more than that. See Wikipedia ...
. And I'm not even sure that this list is actually exhaustive ( note how things that are very different like the intervention in the suppression of the Greek Communist partisans, the failure of Bay of pigs and the Invasion of Granada are put together for instance ).
http://en.wikipedia.org/wiki/List_of_wars_involving_the_United_States The very nature of empires is to wage wars, even against their allies ( many Europeans for instance think that there is kind of monetary war going on for instance ) if needed.
stoicsentry: Someone should try to figure out between Rome, the U.S. and Britain who has fought the most wars. I suspect Rome still has U.S./U.K. beat. Let's hope it stays that way... *sigh*
As for the Romans, the wikipedia list is far from exhaustive. No only there are many more mentionned in the various texts that made it to us ( like the war against the Sarmatians in the IIIrd century, or Marcus Aurelius campaign one the Danube, or Aureian's campaigns against the Gallic Empire , just to mention the ones that are obvious to me ), but many texts and testimonies have simply been lost. And the list only goes to the division of the Empire. Both the Western and the Eastern Empire had quite a lot of military activity after 395...
So, yes, I'd say that as warmongers go, Rome still beats the USA. But Rome existed for more than a full millenium.