U.S. admiral Matthew Calbraith Perry's naval expedition to Japan in 1853 forced the latter to open up and sign a treaty in a flurry and ended the country's 200-year close-door policy. Through examination of the whole event and the reaction of the Shogun court and motivated daimyos to the warning of the expedition, this paper concludes that Japan's opening up looked accidental but actually came as inevitable. The reasons lie in the fact that, in the mid-19th century, capitalist countries were expanding globally and Japan's being involved in the capitalist world market in the making was unavoidable. Japan's loose vassal system and escalation of class conflict at the time damaged the authority and stability of the rule of the Tokugawa shogunate. When confronted with external forces, Japanese already had a sense of crisis, and were talking about opening up before the Perry expedition. The "marginality" of traditional Japanese culture is conducive to its absorption of foreign cultures, which would then wake up Japanese intellectuals and induced their ideas of breaking out of the feudal cage.