The Mouse That Roared 1959

They're taking over the country in an invasion of laughs!

Directed by Jack Arnold

The Duchy of Grand Fenwick decides that the only way to get out of their economic woes is to declare war on the United States, lose and accept foreign aid. They send an invasion force (in chain mail, armed with bows and arrows) to New York and they arrive during a nuclear drill that has cleared the streets.