To date, there is no evidence that nuclear weapons or the materials needed to make them have ever fallen into the hands of a terrorist group; even large and sophisticated terrorist groups that have tried to get nuclear weapons have failed to do so; and the international community has taken a wide range of actions over the past quarter-century (and particularly over the 2010-2016 period of the nuclear security summits) that have drastically improved the security measures for nuclear weapons and materials around the world