The Argentinean Invasion of Brazil in March of 1980 is regarded as one of the critical episodes of the lengthy Brazilian War. The invasion is generally regarded as being caused by the undeclared war having been fought for months along the border between the two countries and the shooting down of Argentinean airplanes by Brazilian government forces throughout 1978 and 1979, including a commercial airliner on February 27, 1980. The rapid mobilization and assault against Brazilian forces amassed against the border occurred starting in the middle of the night and was followed that afternoon by a formal declaration of war by Argentinean President Isabel Perón.
The Argentinean attack, code named Operación "Bola de Fuego" (Operation Fireball), resulted in the land and sea invasion of southeastern Brazil (Cisplatina Province), bombing attacks at previously undisturbed Brazilian military targets in the south, and the destruction of Brazilian nuclear weapons facilities secondary to the Cochimbo facility destroyed in US airstrikes in 1983. The attack also opened up a second front in the war, established a formal alliance in May between Argentina and Colombia, and weakened Brazilian military defenses around its more settled southern population centers. In the initial attack in 1980, as many as 12,000 Brazilian soldiers were killed against about 5,000 Argentinean soldiers.
The Argentinean invasion of Brazil was immediately followed by Brazil's counterattack in the fall of 1980, in which they occupied territory in the north of Argentina and land battles were continuously fought throughout the remainder of the war.