France and Vietnam sign the Second Treaty of Saigon, further recognizing the full sovereignty of France over Cochinchina.

The French Third Republic was the system of government adopted in France from 4 September 1870, when the Second French Empire collapsed during the Franco-Prussian War, until 10 July 1940, after the Fall of France during World War II led to the formation of the Vichy government. The French Third Republic was a parliamentary republic.

The Nguyễn dynasty was the last Vietnamese dynasty, preceded by the Nguyễn lords and ruling unified Vietnam independently from 1802 until French protectorate in 1883. Its emperors were members of the House of Nguyễn Phúc. During its existence, the Nguyễn empire expanded into modern-day Southern Vietnam, Cambodia, and Laos through a continuation of the centuries-long Nam tiến and Siamese–Vietnamese wars. With the French conquest of Vietnam, the Nguyễn dynasty was forced to give up sovereignty over parts of Southern Vietnam to France in 1862 and 1874, and after 1883 the Nguyễn dynasty only nominally ruled the French protectorates of Annam as well as Tonkin. Backed by Imperial Japan, in 1945 the last Nguyễn emperor Bảo Đại abolished the protectorate treaty with France and proclaimed the Empire of Vietnam for a short time until 25 August 1945.

The Treaty of Saigon was signed on 15 March 1874 by the Third French Republic and the Nguyễn dynasty of Vietnam. Vietnam made economic and territorial concessions to France, while France waived a previous war indemnity and promised military protection against China. The treaty effectively made Vietnam a protectorate of France.

Cochinchina or Cochin-China is a historical exonym for part of Vietnam, depending on the contexts, usually for Southern Vietnam. Sometimes it referred to the whole of Vietnam, but it was commonly used to refer to the region south of the Gianh River.