A pioneering United Nations treaty aimed at regulating the global trade in conventional weapons surpassed a symbolically important threshold on Wednesday when 18 countries, most notably the United States, officially signed the document, pushing the total number to more than half of the organization’s member states.

Proponents of the treaty, which was adopted overwhelmingly by the 193-member General Assembly in April, but still required signing and ratification, said the latest signatures would provide new momentum for putting it into effect. But that goal could still be a year away, some said.

As of Wednesday, the total number of signatures stood at 107. At least 50 of the member states that have signed the treaty must ratify it in order for it to take effect, and so far only six have done so.

The treaty, which took seven years to negotiate, is considered by rights advocates to be a landmark document that would for the first time impose moral standards on the enormous cross-border trade in conventional arms that fuel conflicts around the world, most notably in Africa. It is devised to thwart sales to users who would break humanitarian law, foment genocide or war crimes, engage in terrorism, or kill women and children.