Final answer:
The Enlightenment movement was the main influence on the Founding Fathers when forming the new United States government, as it provided vital philosophical underpinnings for the Declaration of Independence and the Constitution.
Step-by-step explanation:
The main influence on the Founding Fathers when forming the new government was a) The Enlightenment movement. This intellectual movement of the 17th and 18th centuries emphasized reason, individualism, and skepticism of traditional doctrines. Visionaries like John Locke, with his theories on natural rights and social contracts, and Baron de Montesquieu, with his ideas on the separation of powers, heavily influenced the political thought that shaped the United States. The Founding Fathers, including Thomas Paine, Benjamin Franklin, John Adams, and Thomas Jefferson, infused Enlightenment principles into the Declaration of Independence and the Constitution to justify the rebellion against the British and the establishment of a government that would safeguard the natural rights of its citizens.