Leviathan
Thomas Hobbes · 1651
"Without a common power to keep everyone in check, human life would be a war of all against all — so rational self-interested individuals agree to surrender some of their freedom to an absolute sovereign in exchange for security and order, and that agreement, not divine right, is the true basis of political authority."
Hobbes starts from a thought experiment: the state of nature, a hypothetical condition with no government, no laws, no enforceable agreements. Since people are roughly equal in their capacity to harm one another and resources are scarce, he argues this condition inevitably collapses into a war of every man against every man, making life, in his famous phrase, solitary, poor, nasty, brutish, and short. Escaping this isn't a matter of morality — it's a matter of rational self-interest, since everyone is better off under any stable authority than under permanent mutual threat.
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A Theory of Justice
"A just society's rules are the ones rational people would agree to from behind a veil of ignorance — not knowing their own future race, class, talents, or position in that society — which Rawls argues would lead them to prioritize basic liberties for all and structure inequality so it benefits society's worst-off members."