The English Parliament became bicameral in recognition of the distinction between the nobility and clergy and the common people. When the British colonies were established in America, the colonial assemblies were likewise bicameral because there were two interests to be represented: the mother country, by the governor in council, and the colonists, by their chosen deputies. After the Declaration of Independence in 1776, bicameral systems were established in all the states but Georgia, Pennsylvania, and Vermont. In those three states, single-chamber legislatures were set up, but they were replaced by bicameral legislatures in 1789, 1790, and 1830, respectively. All the new states subsequently admitted into the Union entered with two-house legislatures.
Although the Continental Congresses and the Congress of the Confederation had been unicameral, the Constitutional Convention of 1787 decided that the new national legislature should consist of two branches in order to preserve the identity of the separate states, safeguard the influence of the smaller states, and protect the interests of property.
With the extension of constitutional government throughout the world, most countries set up bicameral legislatures on the English or U.S. models, with large first chambers chosen by popular vote and smaller second chambers whose members were either elected or appointed (or, in some cases, determined by inheritance) and often represented political subdivisions, such as the Swiss cantons. The bicameral plan is usually found in federal governments, such as those of the United States, Australia, Brazil, and Canada, and in quasi-federal governments, such as those of Germany and India.
Theoretically, this dualism in the bicameral system is justified as an application of the principle of checks and balances. A bicameral system is desirable, it has been argued, to avoid hasty and harsh legislation, limit democracy, and secure deliberation. Although the bicameral system remained prevalent in the 20th century, there were reactions against it. Unicameral councils or commissions came to predominate in American cities, which had often been organized along bicameral patterns in the 19th century. Widespread dissatisfaction with American state legislatures led to numerous proposals for a single-chamber system during the second decade of the 20th century, but the adoption in 1934 of a unicameral legislature by Nebraska (effective from 1937) marked the only departure from the bicameral system among the U.S. states.
Constitutional trends after World War II reflected a growing preference for the unicameral system in nonfederal states of the world. Unicameral national legislative bodies were set up in many European countries and several Latin American ones.
In Britain, where the House of Lords had been weakened, and in France, where the Council of the Republic (renamed the Senate in 1958 on the foundation of the Fifth Republic) was practically impotent, the governments operated, in effect, on the unicameral principle. A unitary system of government does not imply a unicameral legislature. Modern constitutional states often retain two chambers even though bicameralism has declined.
