For most of human history, the answer was simple: the government's power came from the sword, or from God, or from being born into the right family. Kings ruled because they were kings. Nobody asked the farmer's opinion, and the farmer knew better than to offer it.
In the 1600s and 1700s, some thinkers proposed a different answer. John Locke, an Englishman, argued that every person is born with natural rights — rights you have just by being human, that no king gave you and no king can take: your life, your liberty, your property. Government, he said, is not a master. It is a deal. People agree to be governed so that their rights will be protected; that agreement is called the social contract. And a government that breaks the deal — that attacks the very rights it exists to protect — loses its claim to rule.
For a hundred years that was theory in books. In 1776 it became the founding claim of a country. The Declaration of Independence put it in one sentence: governments derive "their just powers from the consent of the governed." Not from God, not from birth, not from the sword. From the agreement of the people they rule. You already know the contradiction standing next to that sentence — its writer enslaved people, and most of "the governed" had never been asked to consent to anything.
Here is the part that makes this more than a pretty idea: every group shut out of the deal has used the deal's own words to force the door. In 1848 at Seneca Falls, women rewrote the Declaration line by line — "all men and women are created equal" — and demanded the contract include them. In 1852, Frederick Douglass stood before a white audience and asked what the Fourth of July could mean to the enslaved, holding the country's founding words up against its practice. In 1963, Martin Luther King Jr. told a quarter of a million people that the nation had written a promissory note — a written promise to pay — and had defaulted on it, and that the movement had come to collect. None of them asked the country to become something new. All of them demanded it become what it had already signed.
Consent is not a one-time signature from 1776, either. It gets renewed, or withdrawn, on a schedule: every election is the governed deciding, again, who may govern. That is why the fights over who gets to vote — coming in Question Six — are really fights over this question. Whoever is kept from the ballot has been cut out of the contract.
And the contract has two signatures. If the government's side of the deal is to protect your rights, the people's side is to do the governing: to vote, serve, argue, and keep watch. The last page of this flyover is about that half of the bargain.