'Sonnō jōi!": "Revere the Emperor, expel the barbarians!"
The writing was on the wall long before the wall crumbled. Japan's splendid isolation — splendid in its own eyes — would no longer be accepted. The outside world was growing restless. Nations were reaching out, testing their strength, harnessing new technologies, trading, expanding, colonizing.
Could Japan remain haughtily aloof? An official sakoku (closed-country) policy had been in place since the early 17th century, when Christian missionaries, active in the country for 100 years, began to seem to the ruling shoguns like an advance guard for European imperialists. Up went the drawbridge. Japan became an impregnable fortress — or a black hole, strictly off-limits to all but a handful of Dutch and Chinese traders confined to specific parts of Nagasaki.