At an investor conference this month, the president of American Airlines said, “We love all of our hubs.” He then explained why the world’s biggest carrier loves Dallas-Fort Worth a little more than the others.

He was talking about efforts to increase profits at three major hubs, led by DFW International Airport. But there’s more to the story and it has particular relevance for the leaders of Amazon, who are deep into the search for a second headquarters.

What’s working for American could work for Amazon, and American CEO Doug Parker has said as much.

“The business and economic climate of Dallas-Fort Worth make it an ideal location for a corporate headquarters — for companies large and small,” Parker wrote to Amazon last year.

His letter was addressed: “Dear potential neighbors.”

The contest to land Amazon HQ2 has attracted international attention for over a year, and the online giant has certainly heard plenty of endorsements from local CEOs. (Amazon's request for proposals actually said: "We encourage testimonials from other large companies.)

American has hubs around the nation, and Parker submitted letters of support for other Amazon contenders, including Charlotte, N.C., Chicago and Philadelphia. But the DFW letter was longer and more enthusiastic while the others were addressed: “To whom it may concern.”

Parker touted this region’s “diverse and talented workforce” and the “warm welcome” that he and colleagues received when moving here five years ago. He also pointed out there’s no state income tax.

“The North Texas area is a big plus when we are recruiting people,” Parker wrote.

Such praise may sound predictable, but there's more than happy talk coming from American. The company is investing heavily in new facilities, including a $350 million corporate headquarters that opens next summer and an $88 million operations center that opened in 2015.

It’s added over 5,000 employees in five years, swelling its local workforce to over 31,000. Workers range from baggage handlers to executives, from reservations agents to pilots. The annual payroll is among the biggest in the region.

The world's largest airline also has been beefing up service at DFW Airport, where it has over 800 daily flights to more than 200 destinations in 30 countries. Next year, it plans to add 15 gates at DFW that will allow up to 100 more departures, president Robert Isom said at an investor conference.

“Why am I so excited about DFW? Because in DFW, we have the opportunity for growth,” Isom said.

In general, that’s a good summation of Dallas’ appeal. Companies come here to grow, and since 2010, over 120 new headquarters have opened in North Texas, according to the Dallas Regional Chamber. That total does not include large regional offices added by State Farm, Liberty Mutual, JPMorgan Chase and others.

American’s growth has a special ripple effect, too. By adding service at DFW, it makes the region more attractive to other companies and gives a boost to economic development.

For years, newcomers have cited DFW Airport as a key factor in their relocation decisions. As a large connecting hub, DFW offers more frequent service to more locations, especially to business centers.

On Monday, for example, DFW had 15 direct flights to Seattle, Amazon’s home base, and American had most of them.

For HQ2, Amazon said “important consideration” would be given to travel time and daily flights to Seattle, New York, San Francisco and Washington. In his letter to Amazon, Parker reeled off each of those destinations and noted the advantage of being in the middle of the country.

“Either coast can be reached in just a few hours, enabling out-and-back, same-day business trips,” Parker wrote.

Chicago and its United Airlines hub can make a similar argument, offering lots of flights and a central location. And Chicago beat out Dallas for Boeing’s headquarters in 2001.

Delta Air Lines also has a powerhouse airport in Atlanta — even larger than DFW — and Dallas and Atlanta have sparred over major relocations for years.

All three cities are finalists in the Amazon competition, and their hubs are among their strengths.

Parker was the driving force behind the merger of American and US Airways, which was part of American’s emergence from bankruptcy in 2013. Since then, annual passenger traffic at DFW has increased from 60 million passengers to almost 70 million — and the growth rate is accelerating.

American and its regional airlines account for over 84 percent of the traffic at DFW. That means American pays the lion’s share of infrastructure upgrades, including a $2 billion terminal renewal program that wrapped up recently.

American also has had to respond to increased competition at both DFW and Dallas Love Field. Southwest Airlines is running at near capacity at Love, offering many connections to business centers and its famous customer service.

At DFW, Spirit Airlines has been growing rapidly by offering deep discounts on leisure fares while global carriers have been introducing flights to more international destinations.

In sum, the air travel market is booming in North Texas, and American stands as both a benefactor and beneficiary. And Amazon should know that it's here for the long haul.

American moved from New York to Fort Worth 40 years ago and recommitted to the region after the merger in 2013. It also extended the lease on its DFW property, which hosts the new headquarters, for 99 years.