The Korean War has had far reaching consequences and is a fitting illustration of the Law of Unintended Consequences.
First and foremost, the start of the Korean War saved the Republic of China from annihilation. The US had previously decided to abandon the Jiang regime, only to change its mind after the Korean War began. This would lead to the segregation of Taiwan from Mainland China, a state that continues to exist today, and remains a source of nuclear flash point.
Second, as we know, the Korean War cemented the separation of North and South Korea, and nuclear-armed North Korea today has become a source of anxiety for the US.
Third, the Korean War led to the breakdown in Sino-Soviet relations. The demand for repayment of Korean War equipment supplied to China by the USSR and the withdrawal of Soviet support for China's industries was one of the causes that led to the Great Leap Forward and the subsequent three-year famine of 1958 to 1961. The catastrophe of the GLF directly led to the sidelining of Mao, which in turn led to the Cultural Revolution, effectively shaping an entire generation of Chinese people.
Fourth, the Korean War was a harsh lesson for the PLA. The initial phase of the PVA intervention was a resounding success, resulting in the routing of UN forces from the Yalu river all the way down to Seoul. However, past the 38th parallel, PVA weaknesses in logistics became prominent, and changes in US tactics to exploit those weaknesses resulted in heavy casualties for the PVA. When the PLA fought India and Vietnam in subsequent conflicts, China would unilaterally declare an end to fighting after achieving a strategic advantage. This allowed China to gain substantial leverage in subsequent diplomatic negotiations, resulting in lasting peace along the India and Vietnamese borders.
Fifth, the USSR, which seemed like the big winner shortly after the War, ultimately ended up being the big loser. Stalin's machinations and subsequent demands from Kruschev angered the Chinese leadership, and led to rapprochement with the US. Cooperation and trade between China and the West resulted in wealth for both sides, and contributed to the collapse of the Soviet Union.
Sixth, Vietnamese reunification under Communists rule. The intervention of Red Chinese troops in Korea was fresh in the mind of Americans during the Vietnam War, which is why Mao Zedong promised Ho Chi Minh that if US sent land-invasion force crossing the 17th parallel into North Vietnam, 1 million Chinese troops would cross into Vietnam to fight back the Americans, which is why US only sent bombers over 17th paralel, never a single US troop crossed that border between South and North Vietnam. The US restricting it's operations only to South Vietnam, allowing the Viet Cong a safe haven in Northern Vietnam to recoup and regain strength is one major reason why US could not fully defeat Viet Cong.
Seventh, Peaceful Reunification of Hong Kong with China. The intervention of Red Chinese troops shook British troops, American troops, and sent a message to the whole NATO Alliance that China is a land-force to be reckoned with. That's why Britain voluntarily gave up Hong Kong to China without firing a bullet, because of the experience of fighting China during the Korean War.