This past Wednesday, American Express made an historic U.S. customer loyalty announcement revealing that it is launching a coalition loyalty program called Plentiin the U.S. this coming May. Why was this announcement so historic? Well for one thing, coalition loyalty has thrived for decades in other parts of the world, including Germany, the UK, the Middle East, New Zealand, and just north of the U.S. boarder in Canada. Strangely enough, it has never really caught on here in the U.S....