The construction of California as an American state was a colonial project premised upon Indigenous removal, state-supported land dispossession, the perpetuation of unfree labor systems and legal, race-based discrimination alongside successful Anglo-American settlement. This dissertation, entitled “How the West was Won: Race, Citizenship, and the Colonial Roots of California, 1849 - 1879” argues that the incorporation of California and its diverse peoples into the U.S. depended on processes of colonization that produced and justified an adaptable racial hierarchy that protected white privilege and supported a racially-exclusive conception of citizenship. In the first section, I trace how the California Constitution and federal and state legislation violated the Treaty of Guadalupe Hidalgo. This legal system empowered Anglo-American migrants seeking territorial, political, and economic control of the region by allowing for the dispossession of Californio and Indigenous communities and legal discrimination against Californio, Indigenous, Black, and Chinese persons. The second section of the dissertation focuses on the implementation and obstruction of a Free State status and the process of Reconstruction within the state. This project concludes with an exploration of the rewriting of the California Constitution in 1879. While the 1849 Constitution established American sovereignty by excluding Californios, Indigenous Peoples, and Black Americans from California society, the 1879 Constitution maintained the colonial project and protected white-only citizenship, by providing mechanisms to manage the “imported colonialism” created by the demand for cheap labor and a growing American empire. In California, the construction of the American state depended on the racialization, dehumanization, and criminalization of Californio, Indigenous, Chinese and Black people that ultimately rendered them unworthy of inhabiting the land as citizens. The colonial process that transformed the frontier from a contested Mexican space into an American state, not only structured California society, but also shaped U.S. society, American imperialism in the Pacific World, and U.S. immigration policy in the late-nineteenth and twentieth centuries.