What was one reason the 14th and 15th amendments failed to prevent future racial segregation

They could not be punished. (What I was told and researched.)

Explanation:

The supreme court ruled that Congress was not able to punish a state or states that violated the civil rights of African Americans, even though these amendments were made to correct the injustice from slavery.

the correct answer is "ethnic heritage".

a person's ethnicity can influence a lot the way he/she votes.

in the united states, for example, black people tend to vote democratic. it happens because the society builds a strong division among people, and equals tend to mingle and support equals. black people's votes in a whole will most certaintly lean towards a candidate or a party which supports the fight against racism.