Broad political history of Japan

1600–1868: Shogunate and relative isolation.
1868–1912: Centralization, modernization and emergence as an imperial power.
1912–1945: Parliamentary experimentation followed by military dominance and war.
1945–1952: Allied occupation and democratic reconstruction.
1952–1990: Stable LDP-led politics and rapid economic growth.
1990–present: Mature parliamentary democracy, economic stagnation and demographic decline.

Tokugawa Ieyasu unifies Japan after a long period of civil war and establishes the Tokugawa shogunate in 1603.
The emperor remains the formal source of legitimacy, while real political power rests with the shogun.
Japan develops a highly centralized and hierarchical political order, with regional daimyo governed under the authority of the shogunate.
Foreign contact and trade are tightly controlled, while Japan experiences more than two centuries of relative internal peace.

In 1853, Matthew C. Perry (Commodore Perry) arrives with American warships and pressures Japan to open to foreign trade.
The resulting crisis undermines the Tokugawa shogunate, which is increasingly seen as unable to defend Japan against Western powers.
In 1868, the shogunate collapses and political authority is formally restored to the emperor. (Meiji Restoration)
The new Meiji government rapidly centralizes the state, abolishes the feudal system, creates a modern army and bureaucracy, and promotes industrialization and mass education.
The Meiji Constitution of 1889 establishes a constitutional monarchy and a parliament, though political power remains concentrated among the emperor, bureaucracy, military and political elite.
Japan becomes an imperial power, defeating Qing China in the First Sino-Japanese War (1894–1895) and Russia in the Russo-Japanese War (1904–1905).

During the Taishō period, political parties and the parliament gain greater influence, producing a period often called Taishō democracy.
The military, however, retains substantial independence from civilian political authority.
During the 1930s, economic crisis, political instability and military influence contribute to the collapse of parliamentary politics.
Japan expands aggressively in China and elsewhere in Asia.
In 1941, Japan attacks the United States at Pearl Harbor, entering the Pacific War.
Japan is defeated in 1945, ending its empire and bringing the existing political order to an end.

Japan is occupied by the Allies of World War II, led by the United States.
The occupation dismantles Japan's wartime military and introduces major political, economic and social reforms.
The Constitution of Japan comes into force in 1947.
Sovereignty is vested in the people, the emperor becomes a symbolic head of state, and the National Diet becomes the central institution of government.
Article 9 of the Constitution of Japan renounces war as a sovereign right.
Japan regains sovereignty in 1952.

The Liberal Democratic Party (LDP) is formed in 1955 and becomes the dominant force in Japanese politics.
Japan develops a stable parliamentary system while maintaining a close security alliance with the United States.
Rapid industrialization and export-led growth transform Japan into one of the world's largest economies.
The postwar political settlement combines competitive elections, LDP dominance, economic development and close alignment with the United States.

The collapse of Japan's economic bubble around 1990 begins a prolonged period of slow economic growth and political instability.
The LDP briefly loses power in 1993 and again in 2009, when the Democratic Party of Japan forms a government.
The LDP returns to power in 2012 under Shinzo Abe, beginning another prolonged period of LDP-led government.
Contemporary Japan remains a parliamentary constitutional democracy, with the emperor serving a symbolic role.
Major political challenges include population aging, demographic decline, economic stagnation, and the country's changing security relationship with China and the United States.