 In 1812 , a Siamese @-@ supported young brother of Ang Chan , the King of Cambodia , rose up and seized the throne , which forced the incumbent to flee to Gia Định . In 1813 , Duyệt , with the approval of Gia Long , entered Cambodia with an army of 10 @,@ 000 troops and forced the Siamese army to retreat . He reinstated Ang Chan and built two citadels , Nam Vang and La Liem on Cambodian territory in order to maintain Vietnamese jurisdiction over the nation , which was formally made a protectorate , adding to his prestige . In addition , Duyet 's domestic governance was effective and stabilized the south , which prompted the people to give him the sobriquet Cọp Gấm Đồng Nai ( " White Tiger of Đồng Nai " ) . As Gia Long 's most trusted mandarin , Duyệt often acted as a conduit between the emperor and the European merchants and government delegates who visited Vietnam . In the early 1820s , Duyet dispatched a delegation to seek out British officials in an attempt to buy arms , but the party got lost in storms and were arrested after washing up in Burma . Duyet remained an advocate of hawkish foreign policy after the protectorate over Cambodia was entrenched , advocating an alliance with Burma against Siam , and expressing confidence that Vietnam could defeat Siam and dominate Southeast Asia . 
