J'sar said it well.
And if I an alien and I'm charge how I show my race to mankind. I would not just go and pick the nation with most guns. I would broadcast my existence
world wide, not to one single nation which is responsible only 8% of population on earth. And seeing past how violent they have been in past.
That is if my intention is peaceful one. If I'm about to enslave and exterminate humans. USA would be first to fall.
i hate to burst your bubble but there are few countries that have been less violent. are biggest number of casualties was 600,000 for the civil war, thats a pittance compared to many other countries like the european countries, china, cambodia, russia etc.......there is canada but they only have fraction of our population. if you compare americas history up to and including the current wars you will find a lot less conflict than in europes history as well as asias and africas and south americas. hell the british had a bigger empire than we do now 100 years ago. we have bases everywhere but we only control those bases not a colony with the exception of puerto rico and they consistenly vote against becoming a state because then they would have to pay taxes. the aliens would undoubtedly notice that even with a military superiority we only control a small percentage of the population and land area......thats not exactly the sign of an empire bent on conquering everyone.
america also has the largest communication network including the media which i think would be important if your going to announce your arrival. as for invading im taking out huge population center first like india and china either to kill as many people as possible or to enslave as many as possible to build a army of genetically manipulated, mind controlled super soldiers. if they can get here with an armada the difference between americas military might and ethiopias would be like someone with a bronze age sword going up against a tank or using an iron sword against a tank........either way..........sword guy loses.
im definitely in the camp of it being highly unlikely. when you crunch the numbers the odds are against it big time.