It strengthened the Japanese state by modernizing it, and in the context of the late nineteenth-century, that meant a militaristic, powerful, largely anti-democratic state with a large bureaucracy. By adopting some aspects of the European state model, Japan was also able to further the growth of industry. But, as others have noted, this arrangement was hardly stable, and it certainly didn't lead to stability in the regions, as the military-industrial powerhouse sought to expand its influence into the Asian mainland and the South Pacific in the twentieth century.
This restoration certainly did bring massive changes to Japanese politics, but as other editors have noted, this only served to damage Japan in the long run, as the massive centralisation of power that it ushered in gave too much power to the military that in turn threatened the stability of a kingdom that had know very stable times prior to this restoration.
The Meiji restoration led to greater centralization of power. In particular, it led to a relative diminishment in the power of the samurai class. It also led to a growth in the power of the military and to a growth in power among industrialists. Ironically, the intervention of the U. S. in Japan through Perry's "opening" of the country helped lead to the conditions that would one day make Japan powerful enough to attack the U. S.
It completely changed the political structure by creating the return of imperial government in Japan. However, as number 2 notes this can also lead to instability because one person in charge means many people might still be vying for power, or vying to be the person in charge.
It created a more modern system, but the system was not stable. The constitution that was eventually created gave too much power to the armed forces. The Army could bring any government down by recalling the Army Minister from the cabinet. This helped lead to the militarism that helped push Japan towards WWII.