I will try to reassure you.
You don't tell us in which country your son is going. Europe is maybe more diverse than the Americas put together (from Alaska to Cape Horn). So, don't hesitate to give more details, and I'll be more specific.
This said, there are also some things in common:
. there is a lot less weapons in Europe than in the US. Therefore, the risk of being killed by any crazy guy with a gun, is a lot less prevalent here.
. petty crime (pickpocketing, robberies, burglary, ...) is more common than in most places in the US. The consequence is that your son should avoid showing big amounts of cash, very obvious jewellery, and so on. It is also better, everywhere, not to look like a lost tourist.
. people expect consideration: if you son goes to a non English-speaking country (better for his experience and education), he should learn at least a few words of the local language. Saying hello and a few words in the local language will make people a lot more receptive and friendly when he asks if they can speak English.
. don't panic on langauge issues, many young peolpe speak English. Of course, this varies country by country.
. your son should not try to pay in dollars but in local currency, be it EUR, GBP, SEK, DKK or others.... Paying in dollars will always make people unhappy, and very often resutl in overcharging.
. to travel easily around, your son should consider a Eurail pass or an Interrail card. Do check online about conditions.
. go to bars, restaurants, talk with people, have fun. Avoid McDonalds, and Burger King, they are not the places to discover Europe.
. getting back to your questions, there is no anti-Americanism against individuals. Your son can say he is American and be very safe. It will very often open interesting conversations, and he will realize a lot more Europeans have traveled to the US than Americans having traveled in Europe.
. on the other hand, I don't think it is a good idea for your son to walk around with a 10 meters-wide (30 feet) American flag with banners saying "support our troops", or "I'm very supportive of Bush's war in Iraq"
. staying on a US military base in Italy might be fun, but is definitely not the best way to meet the Italians
Suggestions of places to go is a tough question. Four month is far from being enough to have a glimpse of Europe. I'll dare and give suggestions, more in a geographical order than in a preference order):
. Lisbon, its trams, its bars, and codfish
. Madrid, its architecture and its nightlife
. Sevilla, Cordoba, Granada, for the mix muslim-catholic monuments
. Barcelona, architecure, nightlife, landscape, energy
. Bordeaux, and les Landes, for the architecure in the city, the endless beaches, and, of course, the wine
. Britanny, for the landscape, and climate
. Normandy too, including Roouien and its gothinc cathedral and churches
. Paris, of course, for the architecture, the museums, the nightlife, and the general atmosphere
. Nancy and Strasbourg, clsoe to each other and very different
. French mediterranean coast, from the Spanish border to the Italian border, with very different landscapes, and ways of living. The riviera may be the most well know area but is too urbanized to my taste.
. Geneva, Lausanne and Bern, to discover what is Switzerland, and the disticntive culture of the Swiss
. Northern Italy, the lakes area, the Alps
. Firenze, Pisa, Venezia and all Italian cities for barocco palaces, and thousands of churches
. Roma, for the combination between antiquity and all periods until now
. Slovenia, to realize that a small country can have a lot of interesting things. Ljubljana is a very nice small city too.
. Many poeple say Sarajevo and Dubrovnik are nice places, but I've not been there
. Greece, gloablly for the antiquity. Athens, of course, but also Olympia, Dlephes, and evrywhere else.
. The Greek islands too, for the variety of landscapes
. Istanbul, for the place where East and West meet
. Budapest, for its architecture, the Hugarian language, and the hot bath culture
. Wien, for barocco buildings, pastries,
. Prag, for the whole old city, and the Charles bridge, ...
. Warsaw, although most of the the city has been rebuilt after WWII
. Krakow for the cult of saint John Paul II, and Auschwitz too
. Gdansk for the cult of saint Lech Walesa
. Vilnius, for the architecture and the small city feeling
. Riga, for its city atmosphere, and its mix of influences
. Tallinn, for the city, and its proximity to FInalnd and Russia
. Saint Petersbourg, to experiencea planned xviiith city, and its transition to the xxist century
. Moscow, of course (although I haven't been there for yeas)
. Helsinki, where people are the Mediterranean of the Nordics
. Lappland, northern FInland
. Stockholm, a large city, and capital of the North
. Oslo, a small city
. Northern Norway, for the fjords, and the impressive landscape
. Copenhagen, struggling with Stockholm to be the most attractive place in the area
. Hamburg, the big port of the North
. Berlin, of course, for the feeling of a booming city along with the combiantion of architecture of xixth century, nazi city planning, and remnants of the Wall
. Amsterdam, its canals, its nightlife, its coffee shops
. Bruges, Gand and Antwerpen for their architecture, and sense of fun of the Belgians
. Brussels, for the Belgians, and for meeting all other Europenasin a single place
. London, for the museums, the architecture (from ancient times to xxith century), the nightlife, ... and language easiness
. Wales for the landscape, and the old castles
. Scotland for the same reasons
I think I must have forgotten many places in the above list..... Leaving in January, he will also be able to go skiing, in the Alps (France, Switzerland, Italy, Austria, Slovenia), in the Pyrenees (France, Spain), or elsewhere....
A last suggestion for you: why don't you take the opportunity of having your son in Europe for a while to go and visit him for a week or two. You will eb able to trvael around to and to discover by yourself.
And a last suggestion for your son: call your father, he worries!