Traditional Japanese legend maintains that the Empire of Japan is founded in 600 BC by Emperor Jimmu, a direct descendant of the sun goddess and ancestor of the present ruling imperial family. For that there is now historical evidence. Japan is inhabited by the Ainu. Since the fourth century immigrants from Korea, China and Manchuria enter the archipelago and a Japanese ethnicity develops. Since 710 one could say Japan is a state. Gradually Japan enlarges over the whole archipelago. Since 1185 Japan is de facto ruled by a dynasty of warlords, the shoguns, who dominate the successive emperors. Since a deceee of 1635 all contact with foreign countries is virtually banned.

In 1868 the shogunate is forced to resign and the emperor is restored to power. The feudal system is abolished and numerous Western institutions were adopted, including a legal system and since 1885 constitutional government along quasi-parliamentary lines. This is preluded by the formation by Itagaki Taisuke of the first political party, the liberal Aikoku Koto (Public Society of Patriots). In 1885 the conservative politician Ito Hirobumi becomes the first prime minister. The first parliamant is convened in 1890, during the rule of prime minister Yamagata Aritomo. The main government party is the Taiseikai (Great Achievement Association). Oppositional are the liberal Rikken Jiyu-to (Constitutional Liberal Party) and the Rikken Kaishin-to (Constititutional Progressive Party), later named the Shinpo-to (Progressive Party). Generally the opposition has a majority in parliament. Japan becomes involved in war with the Chinese Empire in 1894-95 over Korea, leading to Japan's domination of Korea and over Formosa (now Taiwan). The government leads to the inclusion of the Rikken Jiyu-to of Itagaki in government. In 1898 the Rikken Jiyu-to and the Rikken Kaishin-to merge into the Kensei-to (Constitutional Politics Party) and its leader Okuma Shigenobu becomes prime minister. The same year the party splits, the more conservatives members forming the Rikken Seiyukai (Constitutional Political Friends Association) in 1900.

In 1901 the bureaucrat conservative Katsura Taro becomes prime minister. This government is responsible for the Russo-Japanese war. After Japan defeats Russia in 1905 Japan is awarded certain rights in Manchuria and in southern Sakhalin. Katsura is the dominant figure in the upcoming decate. Korea is formally annexed in 1910. Japan fights World War I on the side of the victorious Allies, giving it opportunity to expand its influence in Asia and its territorial holdings in the Pacific.

In 1918 Hara Takashi can form a government based only on the Rikken Seiyukai. After the assasination of Hara in 1921, he is succeeded in short terms by Takashashi Korekiyo, Kato Tomosaburo and Kiyoura Keigo. During the 1920s Japan progresses toward a democratic system of government. In 1924 the liberal Kenseikai (Constitutional Association) wins the elections and Kato Takaaki becomes president. An alternance of governments starts. Wakatsuki Reijiro of the Kenseikai becomes prime minister in 1926 and Tanaka Giichi of Ruikken Seiyukai in 1927. The Tanaka government is followed in 1929 by a cabinet led by Hamaguchi Osachi, the leader of the liberal Rikken Minsei-to (Constitutional People's Party, the successor of the Kenseikai). When he resigns because of health reasons, Wakatsuki becomes prime minister again. This cabinet falls soon and Rikken Seiyukai forms in 1931 a new government under Inukai Tsuyoshi.

However, parliamentary government is not rooted deeply enough to withstand the economic and political pressures of the 1930s, during which military leaders became increasingly influential. Japan invades Manchuria in 1931 and sets up the puppet state of Manchukuo. In 1932 Inukai is assassinated during a coup attempt. From then on the military dominates the government, first under Saito Makoto. He forms a national unity cabinet. In 1934 he is succeeded by Okada Keisuke. Military influence on the governments inreases rapidly. From 1937 the nationalist Konoe Funimaro is prime minister. The Japanese invasion of China in 1937 follows Japan's signing of the "anti-Comintern pact" with Germany the previous year and is part of a chain of developments culminating in the Japanese attack on the United States at Pearl Harbor in 1941. Shortly before that attack Konoe relinquishes power to Tojo Hideki, who establishes a clear military dictatorship. He is succeeded in 1944 by Koiso Kuniaki and in 1945 by Suzuki Kantaro. Suzuki tries to move actively to end the war. Under his premiership Japan surrenders unconditionally.

After almost 4 years of war, resulting in the loss of 3 million Japanese lives and the atomic bombings of Hiroshima and Nagasaki, Japan loses all of its overseas possessions and retains only the home islands. Japan itself is placed under international control of the Allies through their supreme commander, Douglas MacArthur. Japan becomes a parliamentary democratic monarchy under American supervision for the first decades. The islands of Ryu Kyu are under American possesion until 1967-1972. Political, economic and social reforms are introduced, such as a freely elected parliament and universal adult suffrage.

The first partisan prime minister is Yoshida Shigeru (1946-1947) of the newly founded Jiyu-to (Liberal Party), the winner of the 1946 elections. The new constitution takes effect in 1947. After the 1947 elections the Nihon Shakai-to (Socialist Party) becomes the largest party and its leader, Katayama Tetsu, becomes prime minister in a coalition government. Inside this coalition the premiership shifts in 1948 to Ashida Hitoshi of the Minshu-to (Democratic Party). His cabinet falls soon and Yoshida becomes prime minister again, which he remains until 1954. Under his premiership Japan regains full sovereignty in 1952. He is succeeded that year by Hatoyama Ichiro of the Nihon Minshu-to (Japan Democratic Party). In 1955 the Jiyu-to and the Nihon Minshu-to merge into the conservative Jiyu Minshu-to (Liberal Democratic Party).

In 1955 the Jiyu-to merges with the Minshu-to into the conservative Jiyu Minshu-to (Liberal Democratic Party, JMt). This becomes the dominating political force and for most of the time the opposition has no real chance to win elections. That total domination by the JMt lasts until 1993. In that period there are 15 prime ministers. Among them are Kiski Nobusuke (1957-1960), Ikeda Hayato (1960-1964), Sato Eisaku (1964-1972), Tanaka Kakuei (1972-1974), Miki Takeo (1974-1976), Fykuda Takeo), Ohira Masayoshi (1978-1980), Suzuki Zenko (1980-1982), Naksone Yasuhiro (1982-1987), Takeshita Noboru (1987-1989), Kaifu Toshiki (1989-1991) and Miyazwa Kiichi (1991-1993).

In 1993 the JMt fails to win a majority. A coalition of new parties and existing opposition parties forms a governing majority and elects as prime minister Hosokawa Morihiro of the new liberal Nihon Shin-to (Japan New Party). His government's major legislative objective is political reform, consisting of a package of new political financing restrictions and major changes in the electoral system. Hosokawa resigns in 1994 and is succeeded by Hata Tsutomu of the Shinshei-to (Renewal Party), leading Japan's first minority government in almost 40 years. He resigns less than 2 months later and Murayama Tomiichi of the Nihon Shakai-to forms a coalition based on his party and the JMt. The advent of a coalition containing the two parties shocks observers because of their previously fierce rivalry. He is succeeded in 1996 by Hahimoto Ryutaro, re-establishing the JMt premiership. The premiership shifts to Obuchi Keizo in 1998 and Mori Yoshiro in 2000. Inside the JMt the reformer Koizumi Junichiro takes over the leadership and becomes Japan's 87th Prime Minister in 2001. The major opposition party is the liberal centrist Minshu-to (Democratic Party).

In the 2003 elections the Minshu-to becomes the largest party in popular vote, but the electoral system keeps the JMt as largest party in parliament. Koizumi can continue his government.