In 1127, Suryavarman II demanded Đại Việt king Lý Dương Hoán to pay tribute for the Khmer Empire, but the Đại Việt refused. Suryavarman decided to expand his territory northward into Đại Việt territory.^[34] The first attack was in 1128 when King Suryavarman led 20,000 soldiers from Savannakhet to Nghệ An, where they were routed in battle.^[35] The following year Suryavarman continued skirmishes on land and sent 700 ships to bombard the coastal areas of Đại Việt. In 1132, he persuaded Cham king Jaya Indravarman III to join forces with him to attack Đại Việt, where they briefly seized Nghệ An and pillaged the coastal districts of Thanh Hoá.^[36] In 1136, a Đại Việt force under Đỗ Anh Vũ counterattacked the Khmer Empire across modern-day Laos with 30,000 men, but later retreated.^[34] The Cham thereupon made peace with the Đại Việt, and when Suryavarman renewed the attack, Jaya Indravarman refused to cooperate with the Khmers.^[36]

After a failed attempt to seize seaports in southern Đại Việt, Suryavarman turned to invade Champa in 1145 and sacked Vijaya, ending the reign of Jaya Indravarman III and destroying the temples at Mỹ Sơn.^[37] In 1147 when a Panduranga prince named Sivänandana was enthroned as Jaya Harivarman I of Champa, Suryavarman sent an army consisting of Khmers and defected Chams under the command of the senäpati (military commander) Sankara to attack Harivarman, but was defeated in the battle of Räjapura in 1148. Another stronger Khmer army also suffered the same wretchedness fate at the battles of Virapura (present-day Nha Trang) and Caklyaṅ. Unable to overwhelm the Cham, Suryavarman appointed Prince Harideva, a Cham royalty of Cambodian background, as the puppet king of Champa in Vijaya. In 1149, Harivarman marched his army northward to Vijaya, besieging the city, vanquishing Harideva's army at the battle of Mahisa, then executed Harideva along with all of his Cambodian–Cham officials and military, therefore ended Suryavarman's occupation of northern Champa.^[37] Harivarman then reunited the kingdom.