Japan is a nation that consists of a group of islands off the eastern coast of Asia. The principal islands are, in the Roman alphabet, Hokkaido, Honshu, Kyushu and Shikoku. Japan also controls many smaller islands, notably the Ryuku chain south of Kyushu, for a total land area slightly larger than California. The climate, however, has traditionally varied from north to south as much as that from Maine to Georgia. Its capital, Tokyo, is the largest city in the world. 
Early signs of human life appeared in Japan around the year 3000 BC. The wild Japanese Bison was an early target of wild game, hunted to extinction within 500 years.
According to tradition, Japan was unified by Emperor Jimmu, the grandson of the goddess Amaterasu, in the year 660 B. C. He conquered Honshu, the largest island, in a series of expeditions starting from his home base of Setsuma in Kyushu.
Japan was closed off from the rest of the world for a long period of time under the rule of a series of military leaders known as Shoguns (see Tokugawa Shogunate), with the sole exception of Nagasaki, where Dutch merchants maintained a permanent trading post. While the Japanese Emperor continued to reign in the old capital of Kyoto, he was more of a figurehead with little more power than he possesses today. The rule of the Shoguns came to an end in the middle of the 19th century during a brief but bloody period of conflict known as the Meiji Restoration. During the Restoration a large number of young samurai from minor families, most notably Himura Kenshin, tired of the government's mishandling of the country and feeling that if action was not taken Japan would be dominated by western countries, initiated an armed revolt to restore imperial rule. Most samurai from the more powerful families sided with the Shogun, fearing that the minor families would replace them if the revolt was successful. Nonetheless, the shogunate was done away with in 1867 and the imperial period began. The capital was moved to Edo, which was renamed Tokyo; by the early twenty-first century, it had become the center of the world's largest urban conglomeration.
The phrase "imperial period" is not meant to imply that the emperor ruled absolutely in the style of Louis XIV or a Russian tsar; indeed, the emperors relied on prime ministers throughout this period. Rather, it refers to Japan competing with European powers and the United States for colonies and influence during the late 19th and early 20th centuries. The high point of Japanese prestige was the Russo-Japanese War of 1904-5, in which Japan became the principal power in Manchuria and consolidated its control of Korea.
Japan's success at this great game would ultimately prove its undoing. By 1936, during the reign of Emperor Hirohito, the Japanese Empire went by the Orwellian title "Greater East Asia Co-Prosperity Sphere." The increasingly powerful Japanese armed forces, partly inspired by European fascists, came to dominate Japanese politics, assassinating politicians whom they deemed insufficiently devoted to the Emperor and nation. For the next nine years, the military leadership installed its own members (such as Hideki Tojo, chief Japanese strategist of World War II) or, occasionally, civilians who were completely identified with their agenda, as prime minister.
Japan is currently the world's most populous constitutional monarchy, fourth largest economy (counting the European Union as one economy), and has the world's third largest defense budget (counting the constituents of the EU as separate states). The current Emperor is Akihito; he will be succeeded upon his death or abdication by Crown Prince Naruhito. The current Prime Minister is Shinzo Abe, of the Liberal Democratic Party. This party is not to be confused with America's liberal Democrats; the corresponding party in Japan is the Socialists. The Liberal Democratic Party has formed all but two of Japan's post-World War II governments, which as in any parliamentary system rise and fall with somewhat less predictability than United States administrations.
Among constitutional monarchies, Japan is likely to be supplanted as most populous by Thailand sometime during the twenty-first century. This is as a result of Japan's low birth rate (in part a result of the nation's early legalization of abortion) and lack of desire to expand immigration (Japan is the most ethnically homogenous of the world's wealthy countries). Ironically, the relative prosperity of Thailand is in large part due to heavy aid and investment by Japan.
As do most constitutional monarchies, Japan has a state religion, Shinto, an extreme interpretation of which helped drive Japan's participation in World War II. However, as in other constitutional monarchies, political involvement with religion is mostly limited to lip service, although symbolic gestures such as the annual wreath-laying ceremony at Yasukuni Shrine have occasionally antagonized Japan's neighbors. Most imported religions are practiced in Japan without interference, and Buddhism and Christianity have been accepted by large portions of the population. Japan has also spawned its share of cults, including the exceptionally lethal but fortunately short-lived Aum Shinrikyo movement of the early 1990's, which in 1994 became the first non-state organization to kill people with nerve gas.