The DSS is the lead U.S. law enforcement organization abroad , and the most widely deployed in the world , protecting 275 U.S. diplomatic missions in over 170 countries and 30 U.S. cities . Originating from diplomatic security measures enacted during the First World War , the agency was formally established in 1985 in response to the deadly 1983 bombings of the U.S. embassy and Marine barracks in Beirut , Lebanon
Marine barracks
1983 Beirut barracks bombings
Diplomatic Security Service