The importance of the Magna Carta in limiting the power of the monarchy lies in its establishment of the principle that everyone, including the king, is subject to the law. Signed in 1215 by King John of England, the document asserted the rights of barons and set precedents for future constitutional developments. It introduced concepts such as due process and the right to a fair trial, influencing later legal frameworks, including the United States Constitution. The Magna Carta is often viewed as a cornerstone of democratic governance.