The United States is not the only country that has mass shootings. Depending on how you want to bend the statistics and how you want to define what is and isn't a mass shooting, it could be said that the United States has a disproportionate amount of mass shootings. Just because we've just accepted that the cartels in Mexico (for example) kill a bunch of people in mass all the time (like 11 dead in two bars in a cartel mass shooting in the last 48 hours) doesn't make it any less of a . . . mass shooting. Obviously that's still not a trophy anybody wants in their trophy case.
But the "It only happens in the United States" trope is simply not reality.