(1) prevent tyranny by acting as a check on power
Branches of government ensures that no one person takes total control of the government. Each branch also has specific responsibilities giving each authority in the government.
Montesquieu was an Enlightenment thinker who believed a government would fall to tyranny when the government or ruler had no one to answer to. By creating a system of branched government, the ruler(s) have a check on their power and have to answer to another body of the government. This system was used in the US under the Constitution by creating three branches of power: executive, legislative, and judicial.