Why did public sector unionization rise so dramatically and then plateau at the same time as private sector unionization underwent a precipitous decline? The exclusion of public sector employees from the centerpiece of private sector labor law—the 1935 Wagner Act—divided U.S. labor law and relegated public sector demand-making to the states. Consequently, public sector employees' collective bargaining rights were slow to develop and remain geographically concentrated, unequal and vulnerable. Further, divided labor law put the two movements out of alignment; private sector union density peaked nearly a decade before the first major statutes granting public sector collective bargaining rights passed. As a result of this incongruent timing and sequencing, the United States has never had a strong union movement comprised of both sectors at the height of their membership and influence.