Why did the Japanese want to take over the port from the Germans so badly? How did it bring them benefits? Overall, what was the role of Tsingtao and its port in World War 1?
I can give a small example of how the Port of Tsingtao was important to the Japanese. EXPORTS.
Basically, starting in the 1890s, textile manufacturing was important for the industrialization of Japan. The industrialization of Japan was important for Japan to compete with Western countries. China was the most important market for textile exports. The expansion of the textile export market to China from the 1890s to the 1910s was dramatic (30% of textile exports in 1900 vs 78% in 1910). The majority of these went through Shanghai and Tsingtao.
Therefore, the Japanese had a clear economic incentive to control the port.
SOURCE: Japan's Total Empire, Louise Young 1998 (pp 190-191)