BETHLEHEM, Pa. - Bethlehem Steel Corp. used to dominate the Lehigh Valley long before it was replaced by the Sands Casino Resort Bethlehem in 2009.

Now the valley is home to behemoth distribution centers for Amazon, Walmart, Zara, Uline, and Primark - just to name a few - that have moved in over the last two years.

FedEx is building a nearly one million-square-foot distribution hub along Route 22. The $335 million warehouse is expected to be completed next year and fully operational by late 2018.

The landscape resembles a giant warehouse farm, with one center rising next to another.

Huge trucks can be seen pulling in and out of the parking lots of these centers - part of the region's role in distributing goods and services that are increasingly being bought over the internet with the promise of a speedy delivery.

Several factors have made the Lehigh Valley the East Coast's chosen distribution hub. These include lots of open land to accommodate those sprawling warehouses, a nearby airport, and not least, a central spot on the Northeast's highway network.

With brick-and-mortar stores racing online retailers to make the speediest deliveries, Bethlehem is ground zero in the battle for customer loyalty.

To grasp the scale of this influx, bear in mind that two million square feet would take up about 34 football fields. Both Walmart and Amazon have more space than that - 2.2 million square feet each.

Uline shipping supplies and the supply-chain firm NFI Industries of Cherry Hill each have centers with close to 1.7 million square feet, while Home Depot has one at 1.3 million square feet.

Primark's warehouse measures just 677,000 square feet, a mere 12 football fields.

"This depot was a cornerstone to our plans in launching our business in the Northeast," said Jose Luis Martinez de Larramendi, president of Primark U.S. Corp. Primark is a lower-cost apparel retailer based in Dublin, Ireland, that entered the U.S. market last year.

The Bethlehem center supplies all Primark East Coast stores. It receives on average 7,000 cartons or sets a day and 35,000 a week. The merchandise comes from Asia, Turkey, and some U.S.-based suppliers.

"The depot makes it possible for Primark to service the U.S. market in the same way it does in Europe," de Larramendi said. "We have product available at all times, and are able to react to trend changes instantly. This gives the U.S. customer the same Primark experience as we offer everywhere else."

Two Walmart warehouses, measuring 1.2 million and 1.0 million square feet each, sit next to Primark's, and employ 650 workers combined.

"There's certainly a very dense talent pool of folks in the area who are very experienced in working for a fulfillment center," said Walmart spokesman Ravi Jariwala. His company has centers outside of Indianapolis, Atlanta, and the Dallas-Fort Worth areas, in Southern California, as well as in Florida.

"Any one of them allows us to serve a pretty significant portion of our customers pretty quickly," he said. "E-commerce is growing quite fast, and we have plans to further accelerate that."

The market has grown three million to five million square feet a year in warehouse space since 2014, according to the region's largest commercial real estate firm, CBRE Inc. It has gone from 50,000-square-foot warehouses to 500,000- to one million square feet plus - and with that, the need for a larger workforce to staff them.

John Lamirand, a research specialist at the Lehigh Valley Economic Development Corp., found that there are 17,281 jobs in the Lehigh Valley involving truck transportation, warehousing, and storage industries - 258 percent above the national average.

Lamirand also said these same industries are projected to grow 32.9 percent over the next 10 years, compared with a projected national average growth of 13.3 percent.

Average earnings per job in this sector for the Lehigh Valley - which includes Northampton and Lehigh Counties - is $51,684, compared with the national average of $56,194.

Why has Bethlehem become so popular? Because drivers "can get to more areas in one day from that area," said Todd B. Sussman, senior vice president of retail for Colliers International. "Same-day delivery is a growing trend, and this area can service New England cities all the way down to D.C."

That's because of the valley's proximity to such major arteries as I-78, I-80, I-81, and I-95, said Ira Brown, president of M&T Bank's Philadelphia region, which has three branches in Lehigh County. "Five major Metropolitan Statistical Areas are within a one day's drive of the Lehigh Valley including New York; Philadelphia; Washington; Boston; and Baltimore. This equates to 80 million people, 25 percent of the U.S. population."

Land also is cheaper and more available than in other I-95 corridor areas, such as northern New Jersey, Philadelphia, and Washington, Brown said. He said distribution centers benefit from competitive labor rates and lower taxes than in surrounding markets.

William Wolf, executive vice president at CBRE, said "it's the consumers' need for that instant gratification for next-day or same-day delivery that's fueled the strength of the Lehigh Valley."

"I have watched it completely change, when we used to hunt pheasant in these fields, to now where there are warehouses everywhere," said Wolf, who has worked from Allentown as a broker for 30 years.

"The major cost for any distribution center is transportation," he said. "Second is labor costs, and those include availability and reliability of labor. Real estate represents maybe 5 percent of the equation."

Another factor is the number of truck drivers who "want a dedicated route and want to be home at night like everyone else. Most drivers can have that in the Lehigh Valley in servicing the Northeast."

CBRE's corporate clients leasing warehouses in the valley over the last two years include Inditex's Zara brand with a 280,000-square-foot facility; Kraft-Heinz (265,000 square feet); R.R. Donnelly publishing company (548,000 square feet); Ricoh Copiers (280,000 square feet); Isuzu Trucks (130,000 square feet); Central Garden & Pet (243,000 square feet), and NFI Industries.

"The new FedEx ground facility is going to change the Lehigh Valley because it will enable access delivery for same day/next day with a later drop-off than previously allowed," Wolf said, "which just enables more corporations to fulfill more orders and maintain customer service at a high level that everybody wants."

It certainly suits Johnell Jackson, 41, of Philadelphia, who visits the Willow Grove Park Mall's Primark twice a week. She said she likes the store's vast selection of goods - replenished daily with truck deliveries from Bethlehem - and how quickly the store changes up its fashion offerings.

"I like both, and they have great customer service as well," Jackson, an area retail manager, said this month as she bought $8 pajamas, $2 slippers, and two pairs of ankle boots for $20 each. "The quality of the product is amazing."