America, with the same voice which spoke herself into existence as a nation, proclaimed to mankind the inextinguishable rights of human nature, and the only lawful foundations of government.

Adams frames the United States’ founding as a single, authoritative “voice” that both created the nation and announced universal political principles. The “inextinguishable rights of human nature” points to natural-rights doctrine associated with the Declaration of Independence: rights are inherent, not granted by rulers, and therefore cannot be legitimately erased. By adding “the only lawful foundations of government,” he underscores consent and rights-protection as the basis of legitimate authority, contrasting them with hereditary power or conquest. The sentence also serves a rhetorical purpose: it elevates America’s origin story into a moral claim about what governments everywhere ought to rest upon, not merely a parochial account of independence.