The passage below is the first section of the Fifteenth Amendment. 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.

What groups would have had the strongest reason to object to the ratification of this amendment?

Fifteen amendment was passed by the congress on 26th Feb 1869, it was ratified on February 3, 1870. It granted the African American men the right to vote.  

It  was opposed by activists like Anthony and Elizabeth Cady Stanton because it didn't gave voting rights to women. The American Women Suffrage Association supported this amendment.

explanation:

kill anyone that got in the way