The general psychological principles in the book are applicable elsewhere, perhaps everywhere, and what's discussed in the book has wider relevance. But coz the authors focused on what was happening on US college campuses and in the US specifically, and probably for lots of other sound reasons as well, they framed it as a specifically "American" phenomenon and aimed the book at a US audience. I'd imagine that even in other cultures where very similar trends are happening, there would be differences coz of different cultural traditions, different histories and different material conditions. The US is set apart from a lot of other places coz of factors like its excessive individualism, atomization, consumerism, the mix of cultures and ethnicities, the legacy of US slavery, the huge gulf between rich and poor, and the country's unusual attitudes and laws re free speech, guns, welfare and health care.