This service is based on Fedex's acquisition of Genco, in December 2014. Genco is a 3rd party logistics services company, offering a of logistic services:from the standard warehousing an fulfillment(including 130 warehouses), to being somewhat of an industry leader at handling returns(and e-commerce has a relatively high rate of returns, especially in fashion), to testing and repairing stuff, and than reselling those.

At that time, Fedex also bought a software company that helps other retailers with complex stuff like customs handling.

Maybe a total framework to handle all the physical and regulatory stuff and e-commerce play might need. The stuff that enables Amazon to have such a large selection, and the stuff that enables it to be so good at customer service. And that may have been what triggered Amazon to attack Fedex.