After the Civil War two amendments were added to the U.S. Constitution that explicitly guaranteed the rights of African Americans as citizens. The 14th Amendment (ratified in 1868) prohibited states from denying the "equal protection" of its laws to any person. The 15th Amendment to the U.S. Constitution (ratified in 1870) affirmed that "[t]he right of citizens of the United States to vote shall not be denied or abridged by the United States or by any State on account of race, color, or previous condition of servitude."
Though they were written into the foundational document of our government, these guarantees were not very well secured in the states of the former Confederacy in the decades after Reconstruction. Various legal and illegal tools were developed on the state level to disenfranchise African Americans and other minorities.
One tool particularly favored in Texas was the "white primary," originally established by internal political party rules and later by state law. The basic idea was to explicitly prohibit non-whites (African Americans primarily, but also Mexican Americans in south Texas) from joining the Democratic Party or participating in its the primary elections.
Because the Democratic Party dominated the political systems of all the Southern states after Reconstruction, its state and local primary elections usually determined which candidate would ultimately win office in the general election. Thus, any voters excluded from the Democratic primary were effectively excluded from exercising any meaningful electoral choice.
In Texas after the turn of the twentieth century many local party leaders adopted rules that barred African Americans (and Mexican Americans in south Texas) from voting in Democratic Party primary elections. But, when the Texas Legislature passed a law in 1923 explicitly barring African Americans from participating in the Democratic Party primary, it fired the opening salvo in a two-decade long legal and political struggle whose outcome hinged on whether a party could or should be regarded as a private entity with the right to establish its own internal rules.
The 1923 law was overturned as unconstitutional by the U.S. Supreme Court in Nixon v. Herndon (1927) for violating the equal protection clause of the 14th Amendment. The decision addressed only the facts of the case before it, which concerned state law not the policies of individual political parties. In response the Texas Legislature passed a new law allowing the executive committee of each state party to decide who could vote in its own primary. In Nixon v. Condon (1932), again citing the "equal protection" clause, the U.S. Supreme Court struck down the statute and the executive committee resolution banning African American participation in the Democratic primary.
In response the Texas Democratic state convention adopted a resolution banning African Americans from participating in the Party's primary. Against the advice of the NAACP private citizens in Houston promptly challenged the resolution in court. In Grovey v. Townsend (1935) the Supreme Court unanimously decided that the Democratic Party was a private organization whose state convention could determine membership qualifications. Later, these same Houstonians this time working together with the NAACP fought back, bringing the case of Lonnie E. Smith, a Houston dentist, to the U.S. Supreme Court.
In Smith v. Allwright (1944), eight justices on a Supreme Court with several new members overturned the Grovey decision. The majority concluded that several state laws made the Texas primary more than just a function of a private organization. Instead, these laws made it an integral component of the electoral process. As a consequence, the court ruled, it was unconstitutional to prohibit African Americans from voting in the Democratic primary, including votes for party officials.
Smith v. Allwright did not prevent other attempts to disenfranchise African Americans. But it effectively ended the white primary in Texas, a major step along the path to securing equal voting rights.