Final answer:
The 15th Amendment to the U.S. Constitution granted suffrage to black men, finalizing the civil rights extensions of the Reconstruction Amendments.
Step-by-step explanation:
Suffrage was granted to black men in the United States through the 15th Amendment to the Constitution, ratified in 1870. The 15th Amendment stated, "The 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." This amendment was the culmination of efforts during the Reconstruction Era and was the final step in a series of amendments - following the 13th Amendment, which abolished slavery, and the 14th Amendment, which provided citizenship and equal protection under the law - aimed to extend civil rights to African Americans.