It's quite difficult to find a clear answer that isn't muddled by bias, propaganda, or lack of proof. I know that Edgar Snow, who spent time in Yan'an with the Communist Party during the war, stated in his book that the Chinese Communists fought more bravely than the cowardly Nationalists, who had low morale and retreated easily, and described their guerrilla strategy in a similar manner to how the current Chinese government portrays the events of the war.
However, Snow has been accused of being biased towards the communists, and his books have been accused of being historically innaccurate. Most of the other threads I've read here refute the Chinese Communist Party's claims of having done the majority of the work in the war and instead claim that Mao actively avoided fighting the Japanese and instead was building his forces for a continuation of the civil war after WW2 ended. This to me seems more logical and practical than a small insurgent band that was just on the verge of being wiped out a year before managing to become a big player in the war.
But then again, if the Communists were so insignificant, why did so many prominent figures reach out and even visit Mao in his base in Yan'an? Why did the US perform the Dixie Mission? According to this interview (https://www.japantimes.co.jp/news/2009/04/09/reference/special-presentations/imperial-army-war-vet-haunted-by-horrors-in-china/#.XfWh65NKhWM ) of a Japanese veteran in occupied China, he was executing prisoners after interrogating them on the whereabouts of the Chinese Red Army, so clearly they must have been performing some sort of resistance rather than simply hiding to cause the Japanese to be concerned about them. Is there any other reliable accounts by Japanese veterans in China? Do any of them give a clear answer to which view of the Chinese Red Army's role in the Second Sino-Japanese war was more accurate?
The primary impact of the Red Army under Mao Zedong was not really related to how large of a role they played in expelling or resisting the Japanese, but rather in the role they played in both Chinese nationalism and in mobilizing resistance and resentment to the Japanese among large swaths of the Chinese population in the north.
The Kuomintang and the communists in the north fought the Japanese in very different ways and also behaved in very different ways. While the Kuomintang fought to hold a line against further Japanese intrusion into China (which happened to not include most of the major cities and roadways of China), the communists and Mao largely operated behind the lines in the form of guerilla warfare in the north. The communist forces helped the rural populations, paid for food, even lowered interest rates. They had already engaged in propaganda campaigns with the rural masses, and continued to do so during WW2. The KMT took conscripts, demanded food and supplies without pay, and generally consisted of large land owners and oppositional interactions with the populace.
Lucien Bianco's book, Origins of the Chinese Revolution, 1915-1949, identified political as well as social and economic reasons for the massive growth of the Chinese Communist Party during the war. Bianco was extremely critical of Mao, but even he recognized that the CCP forces fought the Japanese with far more vigor than the KMT forces did. There are a number of factors explaining why, but primarily it is because the CCP forces initially were revolutionaries, and then, as they grew to number in the millions during WWII, Chinese nationalists motivated against absolutely brutal Japanese occupiers. The KMT forces were primarily conscripts who were not treated well (and often not fed). There are many examples of KMT forces abandoning battles, but in the North the communists stayed while the KMT was almost entirely behind the line. The only resistance there was led by the communists.
In terms of politics, World War 2 saw the communists being legitimized by the proclamation of a united front by Chiang Kai Shek. Further, the invasion by the Japanese caused a massive movement of nationalism in China, u ited against the universally hated Japanese occupiers. In the north, the KMT for the most part fled, while the communists stayed to wage guerilla warfare. The Japanese, true to reputation, responded with ever more brutality. This left the masses of peasants to identify the communists as the essence of Chinese national resistance, but more than in a symbolic way, it left the Chinese peasants desperate for some protection from the Japanese, which they found by joining or at least assisting the Red Army.
To more directly answer the question, the guerilla activities were really quite minor. But they continued for so long that they kept Chinese nationalism alive, caused consternation from the Japanese that their imperial role was not settled, and made the CCP the epitomy of resistance. Following the war, when inflation skyrocketed and the plight of the Chinese was extremely severe, and when the KMT was reliant on the US for aid and materials and backed by the less than committed forces described above, the CPP was able to capitalize on its reputation as the true nationalists (and not so much on their ideology) to overwhelm the KMT.
Ah, my type of question.
There are several points here that need to be addressed:
I’ll try my best to give nuance to the above issues.
For most western scholars, the answer is clear: The NRA played the leading role in China’s final victory over Japan, while the PLA also contributed but to a lesser extent. However, there is still debate among Chinese scholars over the question of proportionality. Before the 1980s, the stances of Chinese academics could be easily identified through their residency: those in mainland China argued for the primacy of the PLA, while those in Taiwan stressed the importance of the NRA towards victory. After the 1980s, some continue to argue over the issue, but many have grown tired of the debate and adopted a position that emphasises the equal contributions of both armed forces. This has in some ways been driven by political considerations, as since the 1990s, the CCP government has changed its perception of the Second Sino-Japanese War and gives equal weight to the contributions of the CCP and GMD. This was done in an effort to better cross-strait relations towards the hoped-for reintegration of Taiwan.
The above controversy in turn produced a simple dichotomy that is oft-repeated in historiography. In most books on the war, the PLA is shown to be responsible for guerrilla warfare behind enemy territory, and the NRA responsible for conventional warfare at the frontlines. For many scholars, their stance on proportionality boils down to their emphasis on either guerrilla or conventional warfare - did the PLA tie down more troops in rear areas, or did the NRA fight against more Japanese forces at the frontlines?
In terms of conventional warfare, it is fair to say that the NRA bore the brunt of the fighting. According to official GMD statistics, the NRA was engaged in twenty-two major campaigns, and 1117 major battles in the years 1937-45 (quantitative analysis has always been somewhat of an obsession among Chinese historians). The PLA can only lay claim to one major campaign, the ‘Hundred Regiments Offensive’ in 1940, which after initial successes, was considered a strategic failure by PLA command. Concerning guerrilla warfare, recent research has shown that the PLA did not monopolise the use of guerrilla forces, at least in the war’s initial stages. Yang Kuisong’s article on GMD guerrilla warfare (first published in 2006 in the influential Journal of Studies of China's Resistance War Against Japan, collected and translated to English in the equally influential Battle for China in 2011) shows that considerable GMD guerrilla forces existed behind frontlines in North China until 1940. In South China, while much attention is focused on the Hong Kong-based East River Column, British documents reveal that multiple GMD guerrilla units operated in Guangdong province right up until the end of the war. Current research on the strength and resilience of GMD guerrilla units throughout the 1937-45 period demonstrates there is more complexity to a simple allocation of combat roles to the PLA and NRA.
The post-war CCP was keen on propagandising the cowardice and low morale of the NRA. While some accusations were justified, this is a broad over-generalisation of NRA combat performance. Accusations made against the NRA officer class are mostly accurate. Many were corrupt, poorly educated and entirely unfit for command or staff work. The situation was not helped when 35% of the Whampoa Military Academy-trained (Republican China’s West Point) officer class was wiped out in the Battle of Shanghai at the start of the war. NRA generals gained an unsavoury reputation for fleeing while their troops were engaged, or defecting with whole units. In one particular incident, the longtime warlord of Shandong, Han Fu-ju, fled from Jinan in December 1937 in defiance of direct orders to defend the city. As he continued to retreat, four further orders to stand and fight were ignored - when retreating from the city of Tai’an, Han responded rather snidely (he was quite well-known for his humour):
Nanjing was not defended, why should Tai’an be?
This did not help his case, and he became the most senior military figure to be executed in the Second World War. The correlation between Han’s execution and the improved combat performance of the NRA in 1938 is yet to be disproved. Of course, not all generals were incompetent - Zhang Zhi-zhong recovered from his own accusations of cowardice to become the premier Chinese war hero when he died on the battlefield in 1940. But despite good performances from some officers, the overall bad reputation of the NRA officer class is seen to be well-deserved.
The low morale of NRA troops has often been taken as a fact, not particularly helped by the widespread reportage of unwilling Chinese citizens tied up by recruitment officers and force-marched to the front. Academic work from Hans van de Ven and Chang Jui-te has fundamentally overturned this perception. They argued that the high casualty rates and constant retreats of the NRA were an unfair reflection of the capabilities of ordinary soldiers. Many often them lacked training, were malnourished, and had inferior weapons compared to the Japanese. Despite all these unfavourable factors, the combat performance of NRA recruits was well-regarded by both Japanese and foreign officers. William Slim, the respected British general (known for being Montgomery without an ego) who led allied forces in Burma, had this to say:
The Chinese soldier was tough, brave, and experienced – after all, he had already been fighting on his own without help for years. He was the veteran among the Allies, and could claim up to this time that he had held back the Japanese more successfully than any of the others. Indeed, he registered his arrival in the forward areas by several minor but marked successes against enemy detachments.’
More often than not, the Chinese soldier fight on - to the death. The sacrifices at the Battle of Shanghai are well-known (a big-budget mainland Chinese film set to be released this year was on the NRA 88th Division, whose last remnants covered the withdrawal of troops from Shanghai - unfortunately the airing of the movie seems to have been forbidden due to political concerns), while the entire Sichuanese 122nd Division was wiped out far away from its home province in 1937. Even late into the war, the Chinese soldier was capable of strong resistance: in both the Battle of Changde in 1943 and the Battle of Hengyang in 1944, Chinese forces slowed Japanese advances at considerable expense. The original contingent of 8,300 men from the NRA 57th Division emerged from Changde with only 83 men left.
The combat performance of ordinary soldiers was frequently hindered by poor tactical decisions by officers. When British Colonel Jacobs-Larkcom visited the Zhejiang front in 1944, he was particularly aggrieved by the defence line held by the NRA 79th Division. There was no concealment, no all-round defence and was located on the forward slope, entirely exposed to enemy artillery fire. The shallowness of Chinese defence lines were often commented upon by foreign observers, as it was particularly vulnerable to flank attacks, the preferred Japanese tactic. The Chinese preference of defending urban settlements also led to severe casualties or the surrender of whole divisions, as Japanese forces simply skirted around Chinese defensive lines. The ordinary Chinese soldier was regularly let down by his commanding officer.