The relation between the Socialist Republic of Vietnam and the People's Republic of China and (, ) are mostly negative. Despite their Sinospheric and socialist background, centuries of conquest by modern China's imperial predecessor have given Vietnam an entrenched suspicion of Chinese. Although the PRC assisted North Vietnam during the Vietnam War, relations between the two nations soured following Vietnam's reunification in 1975. China invaded Vietnam in 1979, known as the Sino-Vietnamese War. Cross border raids and skirmishes ensued, in which China and Vietnam fought a prolonged border war from 1979 to 1990, but have since worked to improve their diplomatic and economic ties. However, the two countries remain in dispute over territorial issues in the South China Sea. China and Vietnam share a 1,281-kilometer border that has historically been an intense source of conflict. A 2014 survey conducted by the Pew Research Center showed 84% of Vietnamese were concerned that territorial disputes with China and Cambodia will lead to full-blown military conflict. Anti-Chinese as well as Anti-Khmer sentiments have risen dramatically amongst the Vietnamese.