By the late 1990s the 56 bit key of DES was getting very problematic.
In 1998 the EFF spent $250,000 to build "Deep Crack" (https://en.wikipedia.org/wiki/EFF_DES_cracker)
This is what happens when engineers choose names.
Deep Crack was able to find a DES key in 56 hours.
In 1997 NIST called for proposals for a new Advanced Encryption Standard.
In three rounds NIST and the international scientific community discussed the advantages and disadvantages of the submitted ciphers.
Requirements:
There were 15 ciphers submitted. Five were finalists: