For the first time in 600 years Japan was threatened by foreign aggression. One among many differences between the 19th century American threat and the 13th-century Mongol invasions is this: 13th-century Japan was fiercely militarist, 19th-century Japan was impotently militarist.
What to do? There were two schools of thought. One favored resuscitating the indomitable "Japanese spirit" (yamatodamashii) that had put the Mongol invaders to flight. The other, seeing that as hopeless, proposed Plan B: bunmei kaika — "civilization."
Meaning what? Different things to different people. A thousand years earlier, Japan had been "civilized" by China. Chinese literature, Chinese government, Chinese religion, art, morals, dress, architecture, were absorbed wholesale, indiscriminately. Backward, backwater Japan became a sort of apprentice China. A critical sense, maturing over time, sifted, reshaped, "Japanized" the whole vast inheritance into what the world knows and admires today as "Japanese culture."