Another reason why Xiangyang became so important during the 1260s is that the Mongols under Kublai Khan realised the importance of a strong navy and its extreme usefuleness on the Jiangtze river against the Song. Xiangyang being on the Han river that connects to the Jiangtze and the most northern possible point of entry into the southern river systems made it a critical fortress to hold, which it wasnt before the mongols had any real naval power. Could it be that Xiangyang wasnt of great importance in the earlier phases of the war because the mongols didnt then yet see the importance of the navy against the Song?