Is the military shotgun an american thing?

[Nyles]

We issue the Remington 870P, there's maybe 6 of them in my company weapons lockup. Don't often see them in the field, but there are a few guys that carry them. Most nations have Remington 870s in very small numbers for specialists uses, mainly for SF and MPs / security forces.

That said, until say the 70s the Americans were the only ones that used them on any large scale, except the British in Malaysia who used the Browning A5 in the jungle. The Japanese in WW2 had a few SXSs with bayonet mounts, and I know the Luftwaffe issued drillings to their pilots as survival guns if you want to count those.