There is much truth about the ugly American epithet. We have in many ways taken over the role played by the English in the days of empire. But cultural myopia and loud, obnoxious tourists are not an American monopoly.
I am a native of the American southwest and grew up in blue jeans, straw hats, pearl snap button shirts and on formal occasions string ties. On a recent trip through the monument valley my wife and I stayed in the same hotel as a German tour group. Noisy, complaining about the services and all that. And I understand German imperfectly, but it was clear that they were sure I understood none. I must be clear that not all members of the group shared this behavior, but it was a very large minority.
On a business visit to Europe I spent some time in Vienna. There the Italians tourists stood out with the boorish behavior.
Americans may have more than it's share of travel boors (or may just have the normal complement) but it shares with Empire Era England the power and wealth that makes it more disagreeable.