Final answer:
Thomas Jefferson wrote the Declaration of Independence to unite the colonists against British rule and outline a government protecting inalienable rights, based on Enlightenment principles and grievances against the monarchy.
Step-by-step explanation:
Thomas Jefferson's purpose in writing the Declaration of Independence was to unite the colonists against the British government and articulate a vision of a government based on the protection of inalienable rights such as life, liberty, and the pursuit of happiness.
Drawing on Enlightenment principles and the social contract theory of John Locke, the Declaration served as a formal proclamation of the colonies' separation from Britain. It enumerated the colonists' grievances against King George III and laid out the framework for a new kind of government centered on the consent of the governed.