Final answer:
The major assumption in the first sentence of the Declaration of Independence is the Enlightenment principle that all individuals have inherent equality and unalienable rights, which justifies the establishment of a government based on the consent of the governed.
Step-by-step explanation:
Major Assumption Underlying the First Sentence of The Declaration of Independence
The first sentence of the Declaration of Independence sets the foundation for America's national identity and its values. The major assumption underlying this sentence is the Enlightenment principle that all individuals are inherently equal and possess certain unalienable rights such as Life, Liberty and the pursuit of Happiness. Moreover, it declares that governments are established by the people, for the people, and derive their legitimate powers from the consent of the governed. By stating these principles, the Declaration of Independence emphasizes the notion that sovereignty resides with the people rather than with a monarch or a ruling class, thus advocating for a government that is accountable to its citizens and constructed upon the cornerstone of individual rights and freedoms.