How did the Tokugawa Shogunate stay in power so long?

Japan's Tokugawa (or Edo) period, which lasted from 1603 to 1867, would be the final era of traditional Japanese government, culture and society before the Meiji Restoration of 1868 toppled the long-reigning Tokugawa shoguns and propelled the country into the modern era. Tokugawa Ieyasu's dynasty of shoguns presided over 250 years of peace and prosperity in Japan, including the rise of a new merchant class and increasing urbanization. To guard against external influence, they also worked to close off Japanese society from Westernizing influences, particularly Christianity. But with the Tokugawa shogunate growing increasingly weak by the mid-19th century, two powerful clans joined forces in early 1868 to seize power as part of an "imperial restoration" named for Emperor Meiji. The Meiji Restoration spelled the beginning of the end for feudalism in Japan, and would lead to the emergence of modern Japanese culture, politics and society.