A prequel, if you will, to DrStrangelove.
Faced with economic ruin due to the collapse of its wine-exporting trade, the mythical Duchy of Grand Fenwick declares war on the United States, its prime minister (Sellers) having convinced the Grand Duchess (PeterSellers) that quick defeat would be followed by massive infusions of American aid. Combines dark comedy with zany madcap humor in a (then) unique way. Possibly the basis for TheNorthKoreanProject? ...
Unfortunately for the Duchy of Grand Fenwick, but fortunately for the plot (and perhaps somewhat predictably), they actually defeat the United States of America, leading to all sorts of complications...
Based on a book with the same name by Leonard Wibberly. Other "Mouse" books are The Mouse on Wall Street, The Mouse on the Moon, and The Mouse That Saved the West.