France invaded Mexico over unpaid damages to a pastry shop

In 1838, after Mexican soldiers looted a French pastry chef's shop in Mexico City, France combined this with other unpaid claims by French nationals to blockade Mexican ports and bombard Veracruz. Mexico declared war in response. The nickname makes it sound trivial, but the real stakes were trade debts and territory, and the conflict pushed Mexico further into financial crisis.

— Standard historical accounts, Pastry War — 27 November 1838 – 9 March 1839