The addition of the Fourteenth Amendment was necessary primarily to limit the powers held by the states, prevent unjust treatment, and ensure equal rights for all citizens.
After the Civil War, there was a pressing need to address the systemic inequalities and discrimination faced by formerly enslaved individuals and other marginalized groups. The Fourteenth Amendment aimed to establish a constitutional guarantee of equality and to protect against state actions that could infringe upon the rights and privileges of citizens. This was crucial in preventing states from implementing laws that could lead to discrimination or inequality based on race or other factors, thereby promoting justice and equal protection under the law.
The other options, while touching on various aspects of post-Civil War legislation, do not capture the broader purpose and necessity of the Fourteenth Amendment as effectively as the chosen response.