In constitutional form and in practice, the Japanese national government is parliamentary. Authority is centered in the Diet, and power is held by the parties in the Diet. Unlike the pre-war system, for example, the Diet parties really do choose the Prime Ministers. The post-war party system changed fundamentally in 1955, when the non-socialist parties combined and formed the mammoth Liberal-Democratic Party (LDP). Since its formation in 1955, the LDP has always had a safe majority in both Houses of the Diet. But, from its beginning as a union of several political streams to the present, the LDP has been made up of several rather stable factions. These factions are the key actors in the biennial election of the party president, who naturally becomes the Prime Minister. As a general rule, votes in a party presidential election are on straight lines. So a Prime Minister is chosen by a coalition of LDP factions which controls a majority of votes at the party convention. Furthermore, the factions present nominees for Cabinet posts, and Ministers are chosen from among these nominees. Cabinet posts become rewards for the factions which voted for the Prime Minister, inducements to opposing factions to enter the Prime Minister's coalition, and buffers to soften or weaken the opposition of hostile factions. In short, the struggle over top political leadership in Japan—the president and the top officials of the ruling party, the Prime Minister, and other Cabinet members—is waged by the LDP factions. (The struggle over policy, on the other hand, is waged by other actors, within the framework established by the outcome of the factions' struggle over leadership.) And because of the wide range of opinion within the LDP, the outcomes of the factions' struggle over top political leadership are very important for Japan. A switch from an Ishibashi to a Kishi, or from a Kishi to an Ikeda, is certainly as significant as, say, the replacement of a Laniel by a Mendès-France.
