The other possible factor is that the dominant characteristic of American culture is fear. While the fear levels reached new heights after 9/11, the current “terrorism” bogeyman is merely the successor to “communism” and “subversive anarchists” that existed throughout the twentieth century. And those have long cohabited with the fear of crime, drugs, and anything unusual or different. The world is such a frightening place for Americans that anyone who travels without the protection of a tour group, a family, or at least a spouse or travel companion is subject to risks that few are willing to contemplate. That’s why a common reaction of someone traveling in a family or group who encounters a solo traveler is “you must be very brave.” Conversely, Europeans are less dominated by fear, so they feel free to take trips by themselves if that’s what they want to do.