As a result of the survival of Itō Hirobumi, Japan's course in history was forever changed. In OTL, Japan became a highly militaristic nation during the first half of the twentieth century. Because of this militarism, the Japanese military and government began to focus more on the spiritual aspects of warfare, instead of developing advanced technology and weapons. This caused Japan to fall significantly behind other major nations technologically in certain areas, such as anti-submarine warfare, which contributed to their defeat in WWII.
In this ATL, Japan never became as militaristic as it did OTL. As a result, technological progress continued, and increased, in this post-Hirobumi Japan. Japanese technology quickly came to rival or surpass that of all other major powers in every respect. They became the undisputed masters of air and naval technology until WWII. These technological achievements also strengthened the Japanese industrial base, which enabled Japan to win WWII.