why was the 14th amendment added to the constitution?

Answer 1

Short answer -- protecting newly freed slaves from harsh "black codes"


Explanation:

There were specific events that prompted Congress to pass the 14th amendment in 1866 (ratification was completed in 1868).

It began in part because Andrew Johnson had decided to restore the Confederate states the Union very quickly and with few requirements. They were required to accept the 13th amendment (ending slavery), but otherwise Johnson showed very little concern for the protection of the rights of the freedmen.

As a result, in 1865 Southern states passed "BLACK CODES", whose restrictions on blacks (including requirements that they sign "employment contracts", and harsh penalties for "vagrancy", that effectively reduced many to a state very much like the slavery they had supposedly just been freed from.

Radical Republicans in Congress were incensed and responded with the Civil Rights Act of 1866 and the 14th amendment to PROTECT the rights the black codes threatened.

http://drbilllong.com/LegalEssays/BlackCodes.html
http://www.civilwarhome.com/blackcodes.htm
http://en.wikipedia.org/wiki/Equal_Protection_Clause#Background

Answer 2

It was post-civil war, dealing mainly at the time with citizenship for former slaves...overturned the Dred Scott ruling...