The chronicle Việt sử lược states that the Khmer Empire first sent "tribute" (embassy) to Đại Việt—in fact probably further peaceful trading overtures—in 1012 and 1014.

[11] Much of the Vietnamese southward territorial expansion started by the Lý and expanded by the Trần kings from the 14th century onward came at the expense of Champa which became an increasingly compressed polity.

By the 17th century, the Vietnamese military commander government Nguyễn lords encouraged settlers to push into Khmer territories, eventually wresting the Mekong Delta from the Cambodian court.

[13] The 16th and 17th centuries marked the height of the Kinh people's (ethnic Vietnamese) penetration into the southern Mekong Delta, displacing the Khmers.

Those led by Mạc Cửu (1655–1735) helped settle Hà Tiên while others flocked to Bien Hoa and My Tho, pushing out the Khmers.

[7] By 1775, the Cambodian court had ceded the areas of Preah Trapeang (Trà Vinh), Srok Khleang (Sóc Trăng), and Moat Chruk (An Giang) to the Vietnamese without bloodshed.

[14] A policy of cultural Vietnamization ("Nhat Thi Dong Nhan") was imposed, forcing Khmers to adopt Vietnamese attire, names, and language.

However, Khmer uprisings in southern Vietnam from 1840 to 1845 made this policy of direct rule inconvenient and expensive for the Vietnamese court, which opted to keep Cambodia as a tributary state after the death of Minh Mang.

In 1863, the Thai-raised King Norodom of Cambodia (reign 1860–1904) signed a treaty with the French Empire, granting the latter mineral exploration rights if it would secure the country against Thai and Vietnamese attack.

In the First Indochina War for independence, some Cambodians, including King Norodom Sihanouk, fought against Viet Minh forces because they feared Vietnamese colonial domination.

Referring mainly to Viet Cong operating in the border region, the new Cambodian president Lon Nol declared that all Vietnamese troops in Cambodia must leave, to maintain the country's neutrality.

The North Vietnamese responded to this request (as well as calls for aid from the Khmer Rouge) by invading Cambodia, quickly conquering over 40% of the country.

PAVN forces would engage Khmer Republic troops inside Cambodian borders many more times during this war in support of the Rouge, such as in Operation Chenla II.

[15] Anti-Vietnamese sentiment was high in Cambodia during the Vietnam War; ethnic Vietnamese were slaughtered and dumped in the Mekong River at the hands of Lon Nol's anti-Communist forces.

In 1979, as a result of the Cambodian–Vietnamese War, Vietnam overthrew the Khmer Rouge, occupied Cambodia, and helped the foundation of client state People's Republic of Kampuchea.

Vietnamese occupying soldiers and journalists discovered evidence of the Khmer Rouge's abuses, such as Tuol Sleng prison facility, and widely publicized them.

Prime Ministers Nguyen Tan Dung of Vietnam and Hun Sen of Cambodia personally attended the celebration to unveil the new marker and reaffirmed the two countries' cooperation and friendship.

Protesters burned Vietnamese flag and currency,[24] and included[clarification needed] the Khmer Krom community and Buddhist monks.

[36][37] Previous examples of Cambodian anti-Vietnamese sentiment include the riots after the 2013 national election, which was allegedly "marred by irregularities, intimidation of members and leaders of the opposition parties".

However, a few days before Cambodia's national election, "Nguyen Chi Dzung, head of citizen protection and legal affairs of the embassy's consular section of Vietnam", also criticized Rainsy, the opposition party leader, for "capitalizing on the ethnic issue for political gains".