According to this, the 1st Marine Division was in both North and South Korea, so probably you should just say Bertram died in Korea.
In mid-March 1952 the 8th Army, to whom the Marines were attached, instituted Operation Mixmaster. The operation was a massive redeployment of UN forces designed to put more South Korean Army units on the Main Line of Resistance (MLR). The 1st Marine Division was reassigned to the far western end of the United Nations line defending a 35-mile line that encompassed the Pyongyang to Seoul corridor. For much of the next year, in what would be termed the "Outpost War", action along this line consisted of small, localized actions because much of the fighting revolved around the holding and retaking of various combat outposts along key pieces of terrain. This changed in March 1953 when the Chinese launched a massive offensive across the U.N. line. The heavy fighting continued until the Armistice took effect on 27 July 1953. During the Korean War the division suffered combat casualties of 4,004 dead and 25,864 wounded.