MS-13 was literally founded in the US, in Los Angeles. Their rise to prominence (from small street gang to transnational one) was under the control of a man named Ernesto Deras, who had been trained by US Army Green Berets in Panama while serving in the Salvadorean Special Forces, and then left El Salvador and moved to the US to escape the brutal civil war in El Salvador- a civil war the US did have some involvement in. But MS-13 (and their rivals the 18th Calle) started in the US and then emigrated back to El Salvador.