Months after this summer's brief but brutal fried chicken sandwich battle, rivals are diligently plotting to win the longer war.

Popeyes, which sparked the latest fight with its spicy chicken sandwich in August, is scrambling to bring back the viral sensation "as soon as possible." Chick-fil-A is steadily growing its reach, outselling chicken chains nearly twice its size. And McDonald's franchise operators, who watched the fight from the sidelines, are pressuring their corporate boss to bring the crispy, breaded prize home.

"JFK called for a man on the moon," they wrote in a July letter. "Our call should be a category leading chicken sandwich."

Why all the hype over a fried cutlet on a bun? As visits to fast food restaurants stagnate, rivals are eyeing Chick-fil-A's runaway growth. The chain added about 1,000 locations and nearly tripled its sales over the last decade. With more than $10 billion in sales in 2018, the company has surpassed both Wendy's and Burger King to become the fifth largest fast food chain after McDonald's, Starbucks, Subway and Taco Bell.

"If you have the biggest share of a growing category, that is profits galore," said Michael Haracz, who until August served as McDonald's manager of culinary innovation. "That is exponentially more sales, more buzz, more foot traffic to your restaurant."

McDonald's, which says it is "synonymous with burgers," has reason to worry: Beef consumption has fallen in the United States. Chicken is now the most popular meat by far.

There will be "clear winners," Haracz said, who will dominate the space and scoop up profits — as long as they can keep up with demand.

Thirty-year food fight

Though the fight over fried chicken was especially buzzy this summer, it was part of a dynamic that dates back at least 30 years.

In 1989 McDonald's launched a national "country-style" McChicken sandwich and sparked a fight with Hardee's, then one of the largest fast food chains in the country. "While McDonald`s is touting their new product, it isn't even comparable to our Chicken Fillet Sandwich, which has been on the market since 1979," Hardee's president said at the time, according to a 1989 report from the Charlotte Observer. The newspaper published the story with the headline, "Chicken sandwiches incite fast food war."

Over the ensuing decades, fast food chains have launched and relaunched new iterations of the sandwich. McDonald's has had multiple versions, including premium and limited-time offerings. Within the last year alone, it's served the Ultimate Chicken Sandwich, the Mighty Chicken Sandwich, a spicy BBQ chicken sandwich and the McChicken.

As companies experimented with chicken sandwiches, they occasionally caused a stir. In 2010, KFC made headlines with the Double Down — a limited-time-only cheese and bacon sandwich with two pieces of fried chicken where the bun should have been. (KFC briefly brought it back in 2014 .)

But even though items like the Double Down have gone viral, there may not have been anything quite like the frenzy that happened this summer, when Popeyes launched its national chicken sandwich.

It wasn't that Popeyes wasn't expecting the sandwich to be a hit. It painstakingly researched what would work with customers, and eventually landed on the right combination — a buttermilk battered and breaded white meat filet, topped with pickles and a choice of mayo or a spicy Cajun spread and served on a toasted brioche bun. Popeyes called the sandwich the "biggest product launch in the last 30 years." Felipe Athayde, president of the Americas at Popeyes, told the New York Times that the company had "very aggressively forecasted" demand , and expected to have sufficient supply through at least the end of September — about six weeks after its August 12 launch date. But stores throughout the country sold out of the sandwich within about two weeks.

Many point to a Twitter exchange as the instigator. On August 19, one week after Popeyes sandwich hit stores, Chick-fil-A's official Twitter account posted a message: "Bun + Chicken + Pickles = all the <3 for the original." Popeyes interpreted the message as a jab, retweeted the post and added ".... y'all good?"

The sassy response struck a nerve. It's racked up nearly 87,000 retweets and 324,000 likes, spawned memes and elicited innumerable cry-laugh emojis from social media users. Chick-fil-A didn't take the bait, but Wendy's stepped in and sparred with Popeyes on Twitter to the delight of onlookers.

It's unlikely that the brand war would have made such a huge impact if Americans weren't already interested in fried chicken sandwiches.

"There had always been fried chicken sandwiches," said Kara Nielsen, vice president of trends and marketing for CCD Innovation, a food and beverage consultancy. But she traces the current interest in the item to the 2008 financial crisis.

"One of the things that surged out of that recession moment was an interest in comfort food, as well as a lot of people opening food trucks, creating food stalls," she said. "And so there were definitely a lot of fried chicken sandwiches coming out at that time. And it's never really stopped."

And as fried chicken sandwiches gained local fans, a small, quirky chain was chugging steadily along.

The rise of Chick-fil-A

Chick-fil-A traces its roots back to founder S. Truett Cathy's original diner, Dwarf Grill, which opened in 1946. Cathy opened the first Chick-fil-A in 1967, in the Greenbriar Shopping Center in Atlanta.

For years, the company expanded primarily in shopping mall food courts. Then, in 1986, it opened its first standalone location in Atlanta. Today the chain operates more than 2,400 restaurants in 47 states and Washington, D.C. Other chicken chains are larger — Popeyes, for example, has more than 2,600 US restaurants and KFC has roughly 4,000. But Chick-fil-A outsells them.

Chick-fil-A's first restaurant in Atlanta's Greenbriar Mall in the late 1960s.

Ranked by annual revenue, Chick-fil-A is the fifth largest US restaurant chain after McDonald's, Starbucks, Subway and Taco Bell — all of which have far more stores.

Chick-fil-A's individual stores are more productive than any of its bigger competitors. They pulled in an average of $4.4 million in 2018, well above unit sales at McDonald's or Starbucks, according to Technomic, a company that specializes in research on the food industry.

The chain is also, according to polls and surveys, beloved.

An Axios Harris Poll published in March found that Chick-fil-A had the best reputation among US adults compared to Starbucks, Yum! Brands (which owns KFC, Pizza Hut and Taco Bell), Chipotle, Papa John's and McDonald's. And for the past four years in a row, US teens surveyed by Piper Jaffray said Chick-fil-A was their favorite restaurant.

Customer service and food quality help explain Chick-fil-A's success. But it also has a commercially important X-factor: authenticity.

R.J. Hottovy, an analyst who covers food for Morningstar, said that in recent years, companies that have specialized in a particular product and appear more authentic tend to do better than those that try to appeal to everyone.

Chick-fil-A scores high on authenticity. It has stuck to Christian roots by keeping stores closed on Sundays, for example. But that conservative tradition has also earned backlash. In 2012 CEO Dan Cathy said he opposed gay marriage on religious grounds . That year the company was also criticized for donations made by the WinShape Foundation , which was started by founder Truett Cathy and financed largely by Chick-fil-A profits, to groups some characterized as anti-gay.

Chick-fil-A says that is has "no political or social agenda," and that "everyone is welcome in our restaurants." Still, new stores have been met with protests . Some fans of fried chicken sandwiches may welcome an offering from a purveyor they see as more politically neutral, like Popeyes.

Nevertheless, Chick-fil-A has grown at a steady clip and picked up those devoted followers.

"There's so many people now who have an understanding or a notion of what Chick-fil-A is, even if they never eat there or if they've never seen one," Nielsen noted. "It's become a bit of this mythical thing, and clearly millennials have found it, and found that it fits their bill."

As Chick-fil-A locations pop up in more cities, more people rush to test out their sandwiches. That's helped boost fried chicken sandwich sales — and gotten other fast food chains to pay attention. "This fried chicken trend keeps evolving because companies like Chick-fil-A expand their reach," Nielsen said.

While Chick-fil-A creeps across the nation, one group in particular is trying to defend its territory. McDonald's franchise operators are calling for reinforcements.

A McMission

On July 10 — a month before Popeyes launched its sandwich — the board of the National Owners Association, a group of McDonald's franchisees that formed in 2018, sent out a strongly-worded letter to its members.

"We are finding ways to drive profitable growth," the board wrote. "Yet, we are still losing guest counts. This continues to be a concern."

One reason for the loss, the board argued, is that customers craving a delicious fried chicken sandwich aren't going to McDonald's. They're going to Chick-fil-A.

"A favorite, that our customers want, is a chicken sandwich. Unfortunately, they have to go to Chick-fil-A for it," the board said. "Chick-fil-A's results demonstrate the power of chicken. Yes, we have great Chicken McNuggets and our McChicken is a very good product. But we do not compete in the premium chicken sandwich category, either grilled or crispy."

The letter continued with a warning: "Our US Southeast markets' results should concern everyone. You may not have Chick-fil-A's in your market or to the degree they have them in the southeast, but they are coming. And they don't discount."

McDonald's knows how to make chicken into a hit. In the early 1980s, around the time Americans first started losing interest in beef, McDonald's founder Ray Kroc wanted to add a chicken entree to the menu. The company's initial attempts, like a deep fried chicken pot pie, didn't resonate with customers. But eventually, McDonald's landed on a winner: Chicken McNuggets, which launched in 1983, were so successful that by 1985 the chain had become the second-largest chicken seller in the fast food space behind KFC.

"Chicken has been on the radar for quite a while at McDonald's," Haracz said. "There's a variety of chicken sandwiches being tested."

In the third quarter of 2019, traffic at US McDonald's restaurants was down . During an October call discussing the earnings, one analyst wondered whether McDonald's lost sales because it sat out the great chicken sandwich war.

"I think it's fair to assume with everything going on in the quarter with chicken that we would go a little bit the opposite way on chicken. So I think that's a fair conclusion," answered Kevin Ozan, the company's chief financial officer.

For now, McDonald's is keeping its plans close to the vest. The company declined to tell CNN Business when it expects to launch its next chicken sandwich, but noted, "We are inspired by the customer demand for premium chicken sandwiches, and are working closely with our franchisees to deliver what our customers want. Stay tuned."

A source close to the conversation between the owners and McDonald's leadership said a premium chicken sandwich may start rolling out as soon as this year.

But while McDonald's tinkers and focuses on other areas of the business, its franchise owners have been getting impatient.

In late August, after Popeyes' massively successful launch, Blake Casper, NOA's director, sent out another somber note.

"It was a busy week, especially if you work at Popeyes," he wrote. "Popeyes came out with a chicken sandwich that rivals Chick-fil-A. It's the first time Chick-fil-A has blinked, or more accurately, was forced to blink. But make no mistake, they blinked. Wendy's got into the action and unfortunately, we're still not in the game."

But, Casper continued, it's not over yet.

"That is going to change. We are working on a chicken sandwich that will compete. We will be in the game. People will tire of the service at Popeyes and they want an alternative to Chick-fil-A," he said.

"They want a chicken sandwich at McDonald's. We are going to give it to them."