Cambodia became a constitutional monarchy under King Norodom Sihanouk. When French Indochina was given independence, Cambodia lost hope of regaining control over the Mekong Delta as it was awarded to Vietnam. Formerly part of the Khmer Empire, the area had been controlled by the Vietnamese since 1698, with King Chey Chettha II granting the Vietnamese permission to settle in the area decades before. This remains a diplomatic sticking point with over one million ethnic Khmers (the Khmer Krom) still living in this region. The Khmer Rouge attempted invasions to recover the territory which, in part, led to Vietnam's invasion of Cambodia and deposition of the Khmer Rouge.