However, not all nations have been willing to cooperate with disclosing or demilitarizing their inventory of chemical weapons. Since the start of the worldwide efforts to destroy all existing chemical weapons, some nations and terrorist organizations have used and threatened the use of chemical weapons to leverage their position in conflict. A notable example includes the use of such weapons by the US government that sprayed more than 20 million gallons of various herbicides over Vietnam, Cambodia and Laos from 1961 to 1971.