S3: What role did initiative play for UN Forces in the Pusan Perimeter and their subsequent breakout?

As 1LT(P) Ward mentioned, MacArthur regained initiative with his landing on Incheon with the plan to cut NKPA’s supply lines and reestablish ROK control of Seoul. The initiative was gained as the Marine Brigade under General Craig and 24th Division under General Church attacked the enemy bulge east of Naktong. By August 19, the Marines and troops from 34th Infantry could find no enemy east of Naktong, indicating that the first battle of Naktong Bulge was a complete American victory. With the help of Fifth Air Force, NKPA, specifically the 4th Division under Lee Kwon Mu, was experiencing enormous difficulties with resupplies of food and ammunition. Under these advantageous conditions, the U.N. was able to retreat and counterattack more quickly than the NKPA whenever NKPA had made breakthroughs of U.N. lines.