Korea was a UN, rather than NATO, run war against the North Koreans who initiated the war with the approval of both Russia and Communist China. The Chinese entered the war directly in late 1950 after the North Koreans had essentially been defeated and driven back to the Chinese border in disarray.
Initially the North Koreans were equipped with a hodge-podge of former Japanese, Chinese, Russian and American weapons. The Chinese were similarily equipped with weapons like the Russian provided Mosin Nagant, Pssh-41, and various light to heavy machine guns. In some cases troops were not issued a weapon and were expected to pick one up from fallen comrades or the enemy.
The Chinese used large numbers of Thompson SMGs which had been provided to the Nationalists as war aid. They also employed numbers of M1917 Enfields and M1903 Springfields which had been furnished to the Nationalists. Other things, like Inglis produced 8mm BRENs and Browning HPs which were given to the Nationalists in some quantities, also appeared. The Chinese used a miscellany of ex-Nationalist M98 Mausers as well. Initially the Chinese were a foot mobile army with very little in the way of artillery, mortars, and logistics support.
China was not an industrialized nation at this time, so they used raw manpower against the massed firepower on the UN side. Their willingness to commit large numbers of troops and take high losses, as well as their infiltration tactics, allowed some of their early successes. As the war progressed, warfare became more static in nature and the Russians provided considerable additional supplies of weapons and stocks of ammo, incl artillery, mortars and jet aircraft. The Chinese eventually became pretty much bomb-proof by reason of their extensive underground shelters in static positions. Once they got out in the open the UN forces could bring their much more massive firepower to bear on them. The war eventually stagnated in the same positions from mid 1951 to the end in mid 1953 when a ceasefire was implemented.