In the Spirit of Laws, Montesquieu advocates for a constitutional style of government. In this constitutional government, there would be separation of powers between different branches of the central government. Giving specific powers to each branch would ensure that no one portion of the government became too powerful. This idea is known today as the system of checks and balances.
These ideas introduced by Montesquieu inspired different forms of government all over the world, including the United States. Our US Constitution is based on many of these concepts, as we have separation of powers and a system of checks and balances between the judicial, legislative, and executive branches.