What happened
On June 25, 1950, North Korean forces invaded the South. A US-led United Nations force intervened; the Incheon landing in September 1950 reversed the front, and UN forces drove deep into the North. Chinese People’s Volunteers entered the war in October–November 1950 and pushed the front back. Two more years of attritional stalemate followed near the 38th parallel, until an armistice was signed on July 27, 1953.
Background
How the war began is established fact: the North’s invasion of the South is documented in Soviet-era archives. The fighting quickly internationalized, setting a US-led UN coalition against North Korean forces joined by Chinese People’s Volunteers.
Consequences
Total deaths, military and civilian, are commonly estimated around three million, the majority of them Korean civilians; millions of families were separated. The armistice left the DMZ and two hostile states on one peninsula, and the alliance structures it hardened — US–ROK, and China–DPRK ties — shape Northeast Asia to this day.