He later assisted the White Fathers missionaries in East Africa and played an important role in the suppression of the slave trade between 1885 and 1892.

He remained in Rome as a member of the Zouaves after Napoleon III withdrew the French troops from Italy in December 1866.

[1] On 20 September 1870 he commanded the defenders of the Porta Salaria during the unsuccessful defense of Rome against the army of the new Kingdom of Italy.

[3] During the Franco-Prussian War General Athanase Charette organized the French Zouaves as a corps of "Volunteers of the West".

The missionary caravans were menaced by armed slave traders in the Great Lakes region of East Africa.

Later the missionaries abandoned three of the new stations due to attacks by the powerful slave traders Tippu Tip and Rumaliza.

[1] Cardinal Lavigerie was keen on the idea of establishing a central Christian state that could dominate the interior of Africa and ward off the influence of Freemasons, Socialists, Protestants and Muslims.

At one point the kingdom of Buganda was seen as potentially playing this role, and Joubert thought he might have to become "Minister of War to His Black Majesty, Mutesa."

King Leopold II of Belgium decided to focus his efforts on the Congo River, and offered Mpala and Karema to Cardinal Lavigerie for White Fathers missions.

He engaged in skirmishes in March and again in August, where his small force of thirty soldiers armed with rifles came close to defeat.

[8] The constant fighting worried some of the missionaries, notably Father François Coulbois, who were concerned that the slavers might decide to attack the mission itself.

[7] This was a fortified village that he built three leagues from Mrumbi mountain, a days walk from Mpala and 2 kilometres (1.2 mi) from the shore of the lake.

Close at hand he had built a chapel, capable of holding about two hundred people, with a sacristy and sleeping-room at the back for Father Van Oost, a Belgian, who used to come for service from the Mpala mission, about a day's journey to the north.

[11] In January 1889 the mission was cut off from the outside world by Abushiri Revolt against the Germans in Bagamoyo and Dar es Salaam.

[7] Around the end of May 1890, while Joubert was absent, a group of Arabs[a] prepared to cross the Lukuga River[b] about 100 kilometres (62 mi) to the north of Mpala.

[10] By 1891 the slavers had control of the entire western shore of the lake apart from the region defended by Joubert around Mpala and St Louis de Mrumbi.

The Belgians had appointed Tippu Tip as their lieutenant in the region, but Joubert refused to recognize the authority of the slaver.

[7] When the Jacques expedition arrived Joubert's garrison was down to about two hundred men, poorly armed with "a most miscellaneous assortment of chassepots, Remingtons and muzzle-loaders, without suitable cartridges."

[19][c] Jacques asked Joubert to remain on the defensive while he moved north, founded the fortress of Albertville and tried to suppress slaving.

[7] The European press was critical of these actions, described by Le Soir in July 1892 as the "military adventures of Cardinal Lavigerie".

[5] In the mid-1890s the agents of the Congo Free State were directed to assimilate the Christian Kingdom on the west of Lake Tanganyika.

[5] In 1933 a committee in Brussels commissioned the sculptor Jules Jourdan to create a medallion of Joubert based on photographs.