- Chinese resistance was strong and widespread: The Chinese military, despite being poorly equipped and lacking a centralized command structure, was able to use its familiarity with the terrain and the support of the Chinese population to resist the Japanese advance. Chinese guerrilla tactics and the use of scorched earth policies also made it difficult for the Japanese to secure and hold territory.
- Japan chose to focus on a naval strategy: After the initial successes in the early stages of the war, the Japanese military decided to prioritize their naval expansion in the Pacific. This was based on the belief that control of the sea was essential for securing Japan's long-term economic and military interests. As a result, Japan shifted resources and attention away from the war in China, slowing down their progress.
- Diplomatic intervention by the Soviet Union: The Soviet Union, concerned about Japan's growing influence in Asia and its potential threat to its own interests, provided significant military and economic aid to China. This included sending volunteer pilots, tanks, artillery, and other equipment, which helped bolster Chinese resistance.
- Economic difficulties: Japan was facing increasing economic pressure due to the war, and its resources were stretched thin. The conflict's duration led to a rise in inflation and a scarcity of essential goods, which weakened Japan's ability to sustain the war effort.
- China received international support: While the United States and other Western powers initially adopted a policy of neutrality, they began providing financial and military assistance to China as the war continued. This support, though limited, helped China to acquire critical supplies and equipment.
- Underestimating the Chinese resistance: Japan initially underestimated the strength and determination of the Chinese resistance. They expected to achieve a quick victory, but they were faced with a more prolonged and difficult conflict than anticipated.
- Overextension of Japanese forces: Japan had spread its forces across a vast area in China, making it difficult to maintain supply lines and secure all the territory they had captured. This overextension left them vulnerable to counterattacks.