Okay, from my studying of the Red Army during the second Sino-Japanese war, while it is true that the GMD slowed down and stopped fighting major battles, the same could be said of the Red Army (who did not fight as you'ld think under the command of the Nationalists), mainly because it got to the point where they could not fight the japanese to their fullest and worry about the GMD at the same time and eventually while conducting geurrilla warfare was also like the GMD building up and conserving strength to fight the GMD, both sides did this.
However the difference is how they saved strength, while operations like the "Hundred Regiments Offencive" ceased due to the weakening of reserves leaving them vulnerable to bullying form Chiang Kai Shek geurilla fighting and mobile "people's war" continued since these were the most effective way to build up the strength of the Red Army within Japanese occupied territory, gain spies and sympathizors behind Japanese lines.
The CCP started the war with barely 50,000 men on paper, by 1941 they had 500,000 Red Army members and by 1945 1,000,000. and by 1949 outnumbered the Nationalists 3 to 1. All through tactics used in the peoples war.
For example, the red army would liberate a village they might stay for a bit buy some supplies then leave and move on, the village families would pressure their able bodies young adults to join them seeing others doing it inorder to gain prestige. Then they're was the anti-japanese sentiment in the north, anyone who wanted to fight back found the Red Army the best way to do so and joined, became loyal to the Red Army and later on fought the Nationalists.
The Nationalists troops, demoralized from bad leadership, crushing defeats, poor food and clothing, and completely hostile and horrible conditions joined the Red Army at every oppurtunity.
Example: 100 men would be conscripted for the GMD, they would have to walk barefoot for days over many li towards the front, given little training and even less food and clothing would be forced naked into a room marely able to keep 2 families smushed with some 30-100 other soldiers naked and chained hand and foot to prevent desertion.
Many died enroute to the front and those that did make it, seeing death almost every moment and risking their lives for no good purpose joined the Red Army upon capture.
The Red Army generally from 1931 onwards employed these basic rules: it was all voluntary anyone could leave even GMD prisoners.
Officers could not hit you.
And I forget the last one. I think you were garunteed food or something, I forget.
*********************
Okay I just read the previous post and you couldn't be more wrong. Chiang Kai Shek (western spelling) was about to commence his 6th and last encirclement campaign (this was when the Japanese were just beginning to invade China in 1937) however a few months previously, Mao and Chou Enlai had befriended the Manchurian yet exiled warlord (name can't remember) who was employed by the Nationalists to defend Shansi and keep the Yan'an base area contained, however he was pissed off at Chiang for Chiang's refusal to liberate Manchuria (because Chiang then was busy attacking the Jiangsi Soviet Republic), so when the Long March ended and Mao and the surviving Red Army was recuperating in Yan'an he made a deal with the warlord to gain a breathing space and find supplies, money and recruits in Shansi.
However back to the future a bit, Chiang was just about to launch his last and final encurclement campaign to finally in his mind destory the Communist Threat to his regime, but the warlord knowing that the Japanese were a far greater threat arrested Chiang Kai Shek. Chaing's wife and near relatives negotiated with the warlord and the Communists and agreed to forge the Unified Front and fight the Japanese.
Mao did no such thing as holding Chiang at gunpoint and was in no position to do so, it was essentially Chiang's own troops that did it for him.