Explicit exclusion: The 1790 Naturalization Act limited naturalization to "free white persons." The 14th amendment, the Treaty of Guadalupe, the 19th amendment, and the Indian Citizenship Act extended the right to vote (if not always the practice) to African Americans, Mexicans living on the newly U.S. side of the border, women, and Native Americans, respectively. It wasn't until the McCarran Walter Act of 1952, which removed the "aliens ineligible for citizenship" category from immigration law, that all Asian immigrants were able to naturalize and, thus, vote. 

 
Poll taxes and literacy tests: State and local municipalities, largely in the US South, levied taxes on voting and/or required voters to pass written tests before voting, effectively disenfranchising the majority of African Americans in those areas.
 
Felony restrictions: State laws have barred nearly 6 million otherwise eligible adults with felony convictions from voting. These restrictions have stripped 1 in 13 African Americans of the right to vote (New York Times, 11/18/2014).
 
Voter suppression: When the US Supreme Court struck down Section 4 of the Voting Rights Act in 2013, it gave clearance to several Southern states to boldly restrict registration, eligibility, and voting in ways that disproprotionately disenfranchise African American citizens. In 2014, Alabama's new voter ID laws went into effect. In 2015, the state sought to close DMV offices in 8 out of the 10 counties with the highest share of non-white registered voters.

Historical and contemporary structural injustices in democratic participation restrict civic engagement and limit political accountability.