When the King of Siam began claiming territories near those held by the French, Mayréna convinced the nervous colonial administrator to have him lead an expedition into the interior in order to negotiate treaties with local tribes.

To justify this, he argued that the tribes involved were not subjects or vassals of the emperor of Annam (modern Vietnam), and hence had a right to independent statehood.

Mayréna's return to Sedang was thwarted by the French Navy, who blockaded Vietnamese ports and seized his arms as contraband at Singapore.

During his travels to Southeast Asia and Europe, Mayréna awarded dozens of noble titles, orders of chivalry, and assorted medals and paraphernalia to his supporters.

Mayréna (who had earlier converted to Islam and married several local women) died under mysterious circumstances (various reports claim by poisoning, snakebite or losing a duel) on 11 November 1890 at Tioman, Malaya.