Most modern states divide power across three arms: the executive (the president or prime minister and the civil service, who implement and administer laws), the legislature (the parliament or national assembly, who make laws and approve budgets), and the judiciary (the courts, who interpret laws and resolve disputes, including disputes about whether a law itself is constitutional). Separation of powers exists specifically to prevent any single arm from accumulating unchecked authority -- a lesson drawn from historical abuses where rulers who could make, enforce, and judge the law simultaneously faced no real constraint. Checks and balances are the specific mechanisms that enforce this separation in practice: a legislature can block or reject executive actions through budget approval or impeachment, courts can strike down laws or executive orders found unconstitutional, and the executive typically appoints judges subject to legislative confirmation.