Which major responsibility does the department of state have?

Protecting and assisting U. S. citizens living or traveling abroad; Assisting U. S. businesses in the international marketplace; Coordinating and providing support for international activities of other U. S. agencies (local, state, or federal government), official visits overseas and at home, and other diplomatic efforts. Keeping the public informed about U. S. foreign policy and relations with other countries and providing feedback from the public to administration officials. Providing automobile registration for non-diplomatic staff vehicles and the vehicles of diplomats of foreign countries having diplomatic immunity in the United States