Amazon.com Inc. has officially dethroned Walmart Inc. as the biggest global company by revenue, a milestone attesting to the massive scale the e-commerce and cloud-computing giant has achieved since its humble beginnings in 1994 as an online bookseller in Jeff Bezos’ Seattle-area garage.Walmart, which had been the largest company by revenue for more than a decade, on Thursday reported sales of $713.2 billion for the 12 months ending Jan. 31. Amazon, which operates on a fiscal year ending in Dece...