Amazon poses a threat to brick-and-mortar stores. For Walmart, that means fighting back by beefing up its digital portfolio. The chain has been on an acquisition spree lately, snapping up Jet.com, Bonobos, Moosejaw, ShoeBuy and ModCloth, and it is now in talks to acquire Birchbox. Walmart’s e-commerce sales have increased 63% in the first three months of this year, compared to 29% last quarter.