That growth has left companies like FedEx with something of a quandary: keep working with Amazon, even if it could hurt long-term business prospects, or cut ties with the company and try to build a shipping business around other players.

“FedEx has made the decision that is no longer wants to sharpen its executioner’s sword,” said Scott Galloway, a professor at New York University’s Stern School of Business. “It’s another reflection of this winner-take-all ‘Hunger Games’ economy that is dominated by an increasingly few number of companies.”

In just a few years, Amazon has become one of the nation’s largest shipping companies, delivering its own packages and those of small businesses that sell their goods via Amazon’s website. It has transported those packages using its own trucks, planes and delivery staff, particularly during the so-called last mile, the leg immediately before a package is delivered.

During the holiday season in 2018, Amazon handled 30 percent of its last-mile shipments. That was up from 8 percent in 2016, according to an analysis by Rakuten Intelligence, an e-commerce data and analysis provider.

Amazon is also moving more packages through the air. The company is expected to end the year with a fleet of 50 aircraft, up from 40 at the end of 2018. In four years, the company could have as many as 200 aircraft, according to the financial firm Cowen.