The half century before the Civil War was beset with conflict over freedom as well as slavery: what were the arrangements of free society, especially for African Americans? Beginning in 1803, many free states enacted black codes that discouraged the settlement and restricted the basic rights of free black people. But claiming the equal-rights promises of the Declaration and the Constitution, a biracial movement arose to fight these racist state laws. Kate Masur's magisterial history delivers this pathbreaking movement in vivid detail. Its advocates battled in state legislatures, Congress, and the courts, and through petitioning, party politics and elections. They visited slave states to challenge local laws that imprisoned free blacks and sold them into slavery. Despite immovable white majorities and unfavorable court decisions, their vision became increasingly mainstream. After the Civil War, their arguments shaped the Civil Rights Act and the Fourteenth Amendment, the pillars of our second founding.