Oh boy, you have just stumbled across possibly the most controversial topic of the Second Sino-Japanese War other than American involvement.

At the Harvard conference on the Second Sino-Japanese War that gave birth to the book The Battle for China: Essays on the Military History of the Sino-Japanese War of 1937-1945, the role of China in context of the wider Second World War was discussed. As most academic conferences are, there was no consensus. However, I would agree with Tohmatsu Haruo that China was a tertiary theater in WWII.

To start with, one must acknowledge the China theater was a huge drain on Japanese resources and manpower. Even at the end of the war, the total troop strength of Japan in China was around 1.05 million, while expenditures in 1945 reached 3.02 billion yen. In comparison, expenditures in Burma were 390 million yen, and in Japan 5.63 billion yen.

But was this drain actually significant towards the wider Pacific War? Could resources and manpower be used elsewhere? By 1944, Japanese naval power had been severely dented by American submarine and surface warfare. While I would not say that Japanese seafaring ability was completely destroyed, as significant numbers of troops were still transported to Hong Kong for Operation Ichigo, it is true that Japan would have significant difficulty in transferring China-based military forces to Japan or to outlying islands. Even if troops were successfully transferred, the troops based in China were mostly reserve divisions and were of lower quality. Regular army and Kwantung army units had long since been transferred back to the Japanese mainland or to the islands before 1944. Moreover, the extent of increase Japan could have achieved in production capabilities with the expenditure spent on China is questionable, especially in contest with American production.

Indeed, one could even argue that a Chinese collapse due to Operation Ichigo in 1944 made no strategic difference to the Pacific War. The main aim of the operation was to destroy American airfields in China from which B-52s could reach Japan. The operation took vast amounts of territory and caused massive destruction to the Kuomintang military, but once the Mariana Islands were taken, there was no point in staging from China the strategic bombing raids that were so destructive to Japanese production and economy. Conversely, Tohmatsu Haruo argues that events in the Pacific War had a direct impact on the Second Sino-Japanese War rather than the other way around.

So the Sino-Japanese War was not that significant in a wider context, but to China, its eight years of war was significant indeed.