The post-World War Two system of politics and government in Japan is based on parliamentary democracy, i.e. citizens vote for people to represent them in the National Diet (Japan), the nation's parliament, with the government typically formed either from members of the largest political party in the House of Representatives, the lower house of the Diet, or from a coalition of various parties. The upper chamber is known as the House of Councillors. Japan is a constitutional monarchy, with its Head of State being the Emperor (Naruhito since 1st May 2019).
Parliamentary systems go back to the Meiji Restoration, but Japanese party government before World War Two was limited; parties were dissolved in 1940.
The Democratic Party of Japan (DPJ) won a landslide victory in the lower house parliamentary elections in August 2009, ousting the Liberal Democratic Party (LDP) after 55 years of near-uninterrupted rule. However, the party lost heavily to the LDP in December 2012 and in March 2016 merged with the Japan Innovation Party to form the Democratic Party.