The munitions themselves are made in the US, but the raw materials, tooling, and various components in more advanced weaponry have complicated supply chains and are sourced from all over.
The US military is going through massive headaches because domestic supply chains arent able to support the construction of new ships, missles, tanks, aircraft, and other equipment like mobile launchers and uniforms because the domestic production of raw materials and skilled labor required for production have been gutted. Just look at the fiasco that AUKUS is currently undergoing trying to produce submarines. Sure the Navy never technically stopped building it’s ships domestically, but allowing the rest of the domestic shipbuilding industry to collapse has lead to the US being comically inept at at producing serviceable ships.
Free market capitalism is incompatible with national security as capital is only interested in quarterly profits and will sacrifice long term security to meet that goal. Defense contractors have de facto monopolies today and use the threat of going out of business to pressure the Pentagon into giving them massive paychecks to fuck around.
Then why is it the United States of Mexico? Calling them and Canadians just reeks of Manifest Destiny bullshit.