American Express Membership Rewards - Citibank AMEX

can someone explain to me these cards?

http://www.citicards.com/cards/wv/cardDetail.do?screenID=924

An american express card offered by citibank? So what is the relationship between citi and amex? Pardon my stupidity if this is a dumb question

These cards are issued and administered by Citibank the same as any Mastercard or VISA network card. They can be used at any merchant who accepts American Express. The cardholder has no contact with the American Express company, in the same way the consumers have no direct contact with Mastercard or VISA.

Cards processed on the American Express network are issued by Bank of America, Citibank, GE, HSBC and other USA institutions. American Express started to do this in early 1980s, but then Mastercard and VISA adopted rules that prevented their member banks from issuing any card other than their own (with reciprocal exceptions for each other).

American Express sued claiming this was a violation of anti-trust law, won, and has generally excused banks from financial damage payments if they will agree to begin issuing American Express network cards.

thanks. I have been wondering about this for a while.