An interesting example of this is the US modernizations of its military industrial capacity by supply pre- and during WWI. There was intense debate in the international community as to whether non-warring countries could supply nations at war without being considered combatants.

If they aren’t, you can’t neutralize the enemies supplies. If they are, those third countries are effectively part of the conflict.

The US had to take the latter stance because it didn’t have a strong industry to product its own weapons. If it supported nations from buying from non-warring parties, it would be shit out of luck if it had its own wars. So it received a lot of investment from European powers, generating jobs, economic growth, and the funding to expand its domestic production without having to take on debt or wait for a war to break out.

Come its entry into WWI and then WWII, the US had a strong home base of industrial capacity for arms manufacturing.