The Battle of Kapyong —widely considered as the defining turning point of the Korean War involving Australian, Canadian and New Zealand forces against Chinese forces
Battle of Chosin Reservoir —first major battle between Chinese and American forces and is considered a major victory for Chinese forces despite heavy losses.
The ROK — how they went from poorly trained to an effective fighting force with mostly competent leadership
Also JACK, the Joint Advisory Commission Korea, which operated covert operations in the Korean War, widely considered to be one of the first CIA/paramilitary ops group of the Cold War. Others in the Korean War are the Korea Liaison Office which conducted clandestine operations and engaged in the battle of Inchon, 8240th Army unit that setup guerrilla operations units, the UN Partisan Infantry Korea which operated deep in North Korean territory, CIA Special Activities Division in Korea, and many more intelligence/covert action. This is just a jumping off point for anyone interested. Here are a few surface level and OSINT sources:
Pak Hon-yong would be an interesting look and dive since the entire lead up to the Korean War is filled with left wing activists who weren’t extreme enough for the DPRK, but too extreme for the Rhee regime. As well as their fate, since Pak was ultimately executed by the DPRK for claims that he was a American spy.
Further more another interesting thing that would be to look at would be the Hawg Wild incident which might be covered in the WW2 series, but I doubt that since it’s not really talked about. In it a B-29 was shot down by Soviet YAKs over North Korea at the end of WW2.
The first topic really opened my eyes as to the speed they were able to recycle old and abandoned equipment and get it into the Pusan perimeter. Almost no armor or vehicles came from the US those first couple of months due to the distances, production levels, and priority for the European theater. Remember while this was happening the USSR was very active in other parts of the world. Korea was at the end of a 5000 mile long supply chain so quite challenging.
Finally in Incheon today there is a dedicated museum to the landings and victory. The people I met were very friendly and appreciative to US and other UN nations for their liberation. It was touching to see them express their gratitude to Veterans of that war.