Louis-Napoleon is persuaded that invasion of Indochina…

Louis-Napoleon is persuaded that invasion of Indochina is the best course of action by 1857, and French warships are instructed to take Tourane without any further efforts to negotiate with the Vietnamese.

Tourane is captured in late 1858 and Gia Dinh (Saigon and later Ho Chi Minh City) in early 1859.

In both cases Vietnamese Christian support for the French, predicted by the missionaries, fails to materialize.

Vietnamese resistance and outbreaks of cholera and typhoid force the French to abandon Tourane in early 1860.

Fear is growing in Paris that if France withdraws the British will move in.

Also current in Paris at this time is the rationalization that France has a civilizing mission—a duty to bring the benefits of its superior culture to the less fortunate lands of Asia and Africa. (This is a common justification for the colonial policies of most of the Western countries.)

French business and military interests increase their pressure on the government for decisive action.

Thus in early 1861, a French fleet of seventy ships and thirty-five hundred men reinforces Gia Dinh and, in a series of bloody battles, gains control of the surrounding provinces.