Why are many Americans ignorant about the rest of the world?

Before you get offended I didn't say "all" I worked on cruise ships for years with US pengers and they don't know anything about the countries where crew members come from, even been asked if I am speaking English! They are not able to answer questions about history, politics or culture, simple things like "what is the currency in Canada, where is the Eiffel tower etc. They know their states but so what, there's a big wide world out there. I was even told that "Europe" is a small country. I could go on and on but I will say that although quite abrasive New Yorkers do seem the most switched on and in touch with reality. Anti americanism may be wrong but having a superior attitude without knowledge of the world does not help get rid of this.