arsenal of democracy

noun1

1. •
   (figurative) The United States of America, as supplier of extensive materiel support to U.S. allies during World War II; or post-war U.S. as the manufacturer and possessor of the greatest quantity of advanced military weaponry in the world, in the service of defending governments favouring the United States, mostly democracies.

   • In a fireside shout Franklin Roosevelt this week told Business and Labor that they would have to speed up the job of making the U. S. the "arsenal of democracy". — 1941