On April 14, 1951, following MacArthur's dismissal, Matthew Ridgway assumed MacArthur's position and controlled America's war effort from Tokyo. General James Van Fleet moved into Ridgway's old role, getting command of the Eighth Army in Korea, which was now strongly entrenched about 20 miles north of the 38th Parallel. Ridgway had his sights set on the Iron Triangle, one of the North Korean's vital staging areas for attacks against South Korea.
Around this time, the PRC (People's Republic of China) put General Peng Teh-haui in command of its forces, which they continued to deny was an officially sanctioned PRC force. Instead, the Chinese soldiers called themselves the "Chinese People's Volunteers", even though they received orders from Peking and had Soviet advisors, notably Colonel General Terenty Shtykov, the Soviet ambassador to Pyongyang.
On April 22, the Chinese People's Volunteers made a big push against the US/UN/ROK forces. Their aim was to recapture Seoul, but they didn't even come close. A second offensive by the Communists in May fared even less well. Ridgway, having seen his forces pushed back a miniscule amount by two major Chinese offensives, decided the time was ripe for a US counteroffensive. By May 30, the US/UN/ROK forces were back at their entrenchments north of the 38th Parallel. The JCS (Joint Chiefs of Staff) prohibited Ridgway from continuing pursuit of the Communists much beyond the 38TH Parallel, although Ridgway did begin Operation Piledriver, an offensive directed against the Iron Triangle. By June 13, 1951, Operation Piledriver had succeeded in taking the Iron Triangle.
With basically a stalemate achieved, in which the Communists could not push against the US/UN/ROK line and the US would not allow attacks further north, Truman began to push for negotiation to end the war. On May 18, under US guidance, many UN countries began a military goods boycott of North Korea and China, hoping to create pressure for a peace treaty.
Before attempting to negotiate in Korea, the US contacted the USSR through George Kennan. Kennan received assurances that the Soviets would allow negotiations in Korea. Soon afterwards, Andrei Gromyko, the Soviet deputy foreign minister, reaffirmed the Soviet willingness to negotiate. At the end of June 1951, Ridgway sent a broadcast throughout Korea asking for peace talks. Kim Il-sung and General Peng Teh-haui agreed to initiate talks at Kaesong, a site in no-man's land near the 38TH Parallel. The Kaesong talks began on July 8. Although the Communists suggested a cease-fire in the war while the talks went on, the US refused to accept the proposal. Thus, fighting continued as the negotiators haggled at Kaesong.
Under Ridgway and Van Fleet's commands, the so-called "Accordion-War" phase of the war, in which rapid swings in territory took place in a matter of weeks, soon ended. Now, a slow war of entrenchment, attack, and counter-attack began. And this slow pace of war slowed further as negotiations began. Ridgway's strategies were conservative and sound, and attacking Communist forces began to take huge casualties. The April 22 offensive, which pushed the US/UN/ROK forces back only 35 miles, failed to take Seoul and resulted in 10 Communists killed for every 1 US/UN/ROK soldier killed. The British 29 Brigade probably suffered the heaviest casualties, but fought particularly heroically. As a whole, it was after repulsing the April 22 offensive that US/UN/ROK soldiers' self-confidence and morale began to improve. Under Ridgway's conservative strategy, the tide seemed to be turning back against the Communists. Interestingly, in the repulse of the May offensive, US bombers took numerous casualties, perhaps the most decisive use of American air power during the Korean War.
In taking the Iron Triangle, which was the Communist's most important staging area for attacks on South Korea, Ridgway put the Communists on the defensive and dramatically changed the tenor of the war. With 75,000 American killed or injured since the fighting began, the American public was now decidedly against continuation of the war; Truman agreed. Truman now pushed for a return to the "status quo ante bellum" (the state of things in Korea before the war started): a Korea divided at the 38TH Parallel. Truman, however, would always refuse to budge on the question of the fate of Formosa, and as a result negotiations ended up taking over a year. The slow pace of negotiations was further influenced by the symbolic importance of Korea in the Cold War: neither side in the negotiations wanted to seem too eager to settle for peace, because to do so might be seen as a sign of weakness.
Since the US wanted to end the war as badly as the Communists, why did it refuse to agree to a cease-fire while the negotiations at Kaesong took place? The reason is that the US thought it had the upper hand in the fighting, and could use strategic bombing to exert pressure on the negotiations. In Operation Strangle, Ridgway had US bombers target crucial parts of the Communist supply line such as roads and bridges. However, Operation Strangle never seemed to have much impact. The Chinese negotiators never showed any sign of responding to the effects of the bombing campaign except maybe to become even more inflexible in their demands. The Chinese resolve partly stemmed from the efficiency and success of Communist forces in repairing damaged roads and bridges, often rebuilding bombed utilities in a matter of hours. Because it was not a highly industrialized country, North Korea had few targets for strategic bombing to take out. (Once again, the failure of strategic bombing in Korea proved to be a foreshadowing of a similar failure in Vietnam.) Another reason the US refused to hold a cease-fire while the Kaesong talks went on was that Ridgway wanted an excuse to send his men into the field, keeping them "fighting trim" instead of allowing them to become inactive and unprepared for battle.