Japanese Politics: Diet System, Parties, and Social Structure

The National Diet and Postwar Political Structure

Under the Occupation led by the United States, Japan underwent legislative changes aimed at providing a more representative political system. Through the Occupation, the Japanese political system was centered in the executive and legislative branches. Created in 1947, the previously known Imperial Diet became the National Diet, composed of two legislative bodies: the House of Representatives (Shugi-in) and the House of Councillors (Sangi-in).

The National Diet became the sole holder of political power in Japan. The Emperor, like the monarchy in Britain, was retained but holds little function or influence over the country's political affairs. In place of the Emperor, the Prime Minister assumed the role of premier ruler. Nevertheless, as a representative political system, the National Diet holds the bulk of legislative control in the country.

The House of Councillors is composed of members of the Upper House; however, despite its nominally higher stature relative to the House of Representatives (Lower House), it has limited power in comparison. The Lower House has the power to choose the Prime Minister, as well as to accomplish legislative tasks such as the enactment of laws, approval of budgets, proposition of amendments, and the checking and balancing of government activities. Though the Upper House can delay or withhold approval of bills proposed by the Lower House, its power extends only to implementing delays—it does not have the power to block or intervene in the ultimate passage and implementation of those bills. The Lower House still determines which bills become law.

From this distribution of powers and the nature of the political system in Japan, it became apparent that the Allied powers—led by the United States and Britain—intended to prevent Japan from returning to the authoritarian regime it had maintained during the Second World War.

Evolution of Japan's Multi-Party System

Japan's political party system had been strong in nature even before the United States occupied the country and introduced political changes. Under the Imperial Diet, Japan had already operated a two-party system, and during the early twentieth century—as early as 1918—the country had been undergoing political shifts toward constitutional governance, wherein power was concentrated among members of the Lower House.

When postwar Japan adopted the new National Diet system, its two-party structure evolved into a multi-party system, driven by the proliferation of new political alliances resulting from various partnerships and associations in business. Japanese politics and business were strongly interrelated during this period. Mobilization of votes began at the political party level, with each party aiming to garner the most votes in order to capture the most seats in the House of Representatives. Over the years, the Liberal Democratic Party (LDP) dominated both the Lower and Upper Houses; however, this trend shifted during the latter part of the twentieth century, when the Democratic Party of Japan (DPJ) was formed around 1996 to challenge the LDP's stronghold in the Lower House. These shifts in political power reflected that vote mobilization begins through political parties and ends with the capturing of seats in the House of Representatives, where the power of the National Diet is centered.

The LDP, as the oldest and strongest political party in Japan by the 1960s, dominated Japanese politics for the next three decades until 1996. Throughout its reign as the majority party of the Lower House, other political parties emerged to challenge its control.

One of the earliest opposition parties was the Social Democratic Party (SDP), formed in 1947 as a counter to the LDP's pro-capitalist principles. Other parties followed—though interestingly, most emerged only after five decades from the SDP's inception. In the 1990s, Japan fully transitioned to a multi-party system. These newer parties included the New Party Sakikage (1993), a coalition formed by LDP dissenters; the New Frontier Party (1995), composed of socio-political organizations that united to challenge the combined control of the LDP, SDP, and Sakikage; and the Japanese Communist Party, which, though founded in 1922, became an active political force only in 1990.

The Democratic Party of Japan was particularly significant because it was able to break the LDP's dominance in both Houses. In the 1998 Upper House election, a radically low voter turnout and declining confidence in the LDP resulted in Diet seats being distributed among multiple parties. The LDP came to share control of both Houses with the SDP and DPJ.