The most important near cause for the downfall of the Nationalists was the eight-year Japanese war, which completely exhausted the government militarily, financially and spiritually. Had there been no Japanese war, the situation in China would have been very different ... [M]any of the disastrous repercussions of the war ... continued to plague the Nationalists during their struggle with the Communists. The price the Nationalists paid to win the Japanese war was also the first instalment toward its eventual downfall.
--From Immanuel Hsu, The Rise of Modern China (Oxford University Press, 1995)
What finally undermined the Nationalist government was not war or politics but economics. The military and political success of the Communists under Mao Zedong certainly played a vital part in determining their takeover in 1949, but it is arguable that the single most powerful reason for the failure of the GMD government was inflation ... By 1949 China’s monetary system had collapsed, the government was discredited, and the people of Nationalist China were demoralised. Even had the Nationalists not been defeated in civil war and driven from the mainland it is difficult to see how Jiang Jieshi and the GMD could have continued to hold power in China.
--From Michael Lynch, China: From Empire to People’s Republic 1900–49, 2nd ed. (Hodder, 2010), p.142.