Bicameral legislatures are popular in federal systems. In a federal system, power is divided between the central government and the states or regions. This means that there are two levels of government that both have their own set of responsibilities and powers. Bicameral legislatures, which consist of two chambers or houses, are often used in federal systems because they provide a way to ensure that the interests of both the central government and the states or regions are represented in the law-making process. The lower house, which is usually based on population, represents the people and their interests, while the upper house, which is usually based on equal representation from each state or region, represents the interests of the states or regions. This system of checks and balances helps to ensure that laws are fair and equitable for all parties involved.