The world’s first international treaty to ban nuclear weapons came into effect on Friday, but experts say that the lack of endorsement from major nuclear powers like the U.S. and China means that North Korea will remain a grave security issue. 

Adopted at the United Nations in July 2017, the Treaty on the Prohibition of Nuclear Weapons (TPNW) aims to put a comprehensive ban on “any nuclear weapon activities,” such as developing, stockpiling or threatening to use nuclear weapons. But major nuclear powers like the United States, China, Russia, and North Korea did not participate in the ratification. 

“[The treaty]