How did Zhu De participate in the formulation of the strategic policy of "developing northward and defending southward"?

After Japan surrendered, it participated in formulating the strategic policy of "developing northward and defending southward", and made major decisions such as adjusting strategic deployment, organizing field corps and implementing strategic transformation. In view of the Kuomintang reactionaries' persistence in the plot against the civil war, they strongly advocated actively developing to the northeast and sending a large number of troops and cadres to occupy the strategic places in the northeast as soon as possible. After Chiang Kai-shek launched a full-scale civil war in June 1946, he served as commander-in-chief of the People's Liberation Army of China and continued to serve as vice chairman of the Central Military Commission, assisting Mao Zedong in directing the national liberation war. In March 1947, the Kuomintang army launched a major attack on the liberated areas. After the Central Committee and the People's Liberation Army headquarters voluntarily withdrew from Yan 'an, they formed a Central Working Committee with Liu Shaoqi and Dong Biwu to carry out the work entrusted by the Central Committee in North China. In the autumn of the same year, he went to the front line in North China to guide the operation. In October, guiding the Shanxi-Chahar-Hebei field army to win the battle of Qingfengdian played a key role in reversing the Shanxi-Chahar-Hebei war situation. In November, he guided the Shanxi-Chahar-Hebei field army to win the battle of Shijiazhuang. This campaign set a successful precedent for the field army to capture the fortified cities. His experience in Shijiazhuang's tough battle was quickly popularized in various battlefields. In May 1948, on behalf of the Central Committee, he attended the enlarged meeting of the front committee of the East China Field Army held in Puyang, Henan Province, and inspected the East China Field Army, making an important speech, which played an important role in strengthening the unity and discipline of the troops. After September of the same year, he participated in the organization and command of the three major battles of Liaoshen, Huaihai and Pingjin, and won a decisive victory in the strategic decisive battle. In May, 1949, China and Mao Zedong issued the Order to March to the Whole Country. The deployment of the campaign to cross the river and the major campaign to liberate the southwest and northwest regions completely overthrew the rule of the Kuomintang in Chinese mainland.