Japan (日本; "Nihon" or "Nippon" in romanized Japanese; meaning "origin of the sun") is the island country in which most of Sailor Moon took place. Japan has a population of over 128 million people over its 3,000 various islands. The main island of Japan is Honshu and the capital is Tokyo, where the series is set.
The word "Japan" probably originated in the Chinese pronunciation of "Nihon" back in the 13th century. Despite discrepancies in the pronunciation over the centuries, both Japan and China still use the identical Chinese characters (漢字; kanji) to represent "Japan" nowadays.
The Japan we know today is the result of modernizing efforts undertaken during the Meiji (明治) Period (1868-1912; "Meiji" meaning "enlightened rule"). For several hundred years, Japan had been largely "closed" to foreign trade and interaction. In 1854, American Commodore Matthew Perry arrived in the Bay of Edo (江戸; the former name of Tokyo) with a fleet of "black ships," as called by the Japanese then, demanding Japan make itself available to trade. The result was a civil war and it was during this period that the Shoguns (将軍), the ruling generals of Japan, lost the seat of power to the Emperor Meiji (明治天皇).
The new generation of Japanese, under the new Emperor Meiji, embarked on a path of "Civilization and Enlightenment" (文明開化; bunmei kaika) to modernize Japan and move from a feudal country to global power. They were successful, and by the early 20th century, Japan had already defeated China (then the Qing Empire, which had a larger modern navy), captured Okinawa (then the Ryukyu Kingdom, a Chinese vessel state) and Taiwan (also known as Formosa, a Chinese province), annexed Korea (another Chinese vessel state; after routing out the Chinese garrison stationed there), and fought Russia to a standstill by defeating the Tsar's navy.
Following the death of Meiji in 1912, his son, the Taisho Emperor (大正天皇; "Taisho" meaning "great righteous"), reigned Japan in a period known as the "Taisho Democracy," whereby the feudal remnants of Japan's Shogunal history (which had resulted in an oligarchy ruling Japan for much of the Meiji Period) began to be brushed off. By the 1931, however, under the reign of Emperor Showa (昭和天皇; "Showa" meaning "promoting peace"), Japan had begun to change drastically, militarizing and expanding into China (quickly occupying the Northeastern Chinese provinces of Manchuria), and signing pacts with the Axis powers of Germany and Italy.
Japan fought against the Allied Powers in World War II, initiating the engagement of the United States into the conflict with the bombing of Pearl Harbor in 1941. The war ended only after Tokyo had been firebombed, and Hiroshima and Nagasaki were destroyed with atomic weapons.
Following Japan's surrender in 1945 was an eight-year occupation by American forces. It was through the occupation that the Japanese military system was dismantled, the Japanese constitution was changed to remove the Emperor as the source of sovereignty and make him a figurehead, and the Japanese industrial complex was broken apart.
Since the end of the occupation, Japan has risen to be one of the world's top global economic powers. The 1950s and 1960s saw an economic boom hither-to unseen in world history. The 1980s were a period known as "the bubble" whereby Japanese real estate prices were artificially inflated to some of the highest on the planet, but following the bubble burst, the Japanese economy entered a decade-long recession.
Emperor Showa died in 1989, and the era of the new emperor has been named Heisei (平成; meaning "peace achieved"). After the burst of the bubble, the Japanese pop culture market (which includes Sailor Moon) has been one of the brightest stars of its economy.