The European Union has begun the process to re-impose restrictions (quarantine, testing) for unvaccinated Americans. The U.S. will be removed from a list of countries whose citizens are allowed to travel freely in Europe without Covid restrictions.
A key consideration for whether and when countries re-impose restrictions is the extent to which their economies rely on tourism. It’s no coincidence that Greece, France, and Spain were among the first Schengen countries to announce they’d welcome Americans before Europe had taken broader action.