The Emperors were stripped of power back in the 12th Century, after the Genpei War and the formation of the Kamakura Shogunate. They remained stripped of power for almost the next seven hundred years; the power struggles were about who would get to be Shogun.
(The logic of the Meiji "Restoration" was essentially "Let's get rid of the archaic Shogunate system that has dominated Japan in one way or another for the last seven hundred years, and pretend we're handing power back to the Emperor where it really belongs.")
yes. what I wanted to say is that the emperor in Japan had a minor role for the longest time, i.e. it had a middle age that was not unlike Europe, with a steady development of warfare techniques and other parts of culture, as well as a constant trickle of foreign influences. Until edo period, where Tokugawa Shogunate was able to grab all power and basically freeze development and shut down borders. In Meiji, Japan industrialized rapidly under a US-backed emperor and with Germany as an ideal. There's a deeper reason why Japan wanted to become a European-style colonial power - because it was already on that path before the 250y stasis anyways, almost taking on Imperial China during Sengoku-jidai.
(The logic of the Meiji "Restoration" was essentially "Let's get rid of the archaic Shogunate system that has dominated Japan in one way or another for the last seven hundred years, and pretend we're handing power back to the Emperor where it really belongs.")