Over the past week, Popeyes has trended on Twitter globally, welcomed expansive crowds and sold out of just about every new chicken sandwich it has. But why is this particular sandwich such a big deal?

The viral success is unprecedented for Americas 19th largest fast-food chain, and its in large part thanks to a competitor nearly triple its size: Chick-fil-A .

Interest surrounding Popeyes chicken sandwich was only gaining light interest when the fried-chicken chain announced the new menu item on Aug. 12. The sandwich promised to excite fans with barrel-cured pickles, a buttery toasted brioche bun, creamy mayo and buttermilk battered and hand-breaded chicken filet, Bruno Cardinali, Popeyes head of marketing for North America, told HuffPost.

But excitement began building Aug. 19, when Chick-fil-A tweeted its way into the conversation, reminding its 1.1 million followers that Bun + Chicken + Pickles = all the for the original .

Popeyes responded with yall good ? and the chicken sandwich wars had officially begun. So, too, had Popeyes sales.

It all started with the high quality of our new chicken sandwich that we launched on Aug. 12; we saw a major boost in organic conversations, and we felt it made sense to jump in and participate, Cardinali explained. After one of our tweets last Monday, we saw another huge spike in conversation about the sandwich. For a time, the sandwich competition was the top trending topic on Twitter in the U.S. and worldwide, he said.

It just so happens that the buzz was largely spurred by Chick-fil-As tweet, which gently launched the Twitter war.

Popeyes said it introduced its new chicken sandwich to meet existing customer demand, but the social media conversation has been bringing hordes of new faces through the fast-food chains doors.

Google searches for Popeyes chicken sandwich grew almost 1,000% following the Aug. 19 tweets, according to Google Trends . Many Popeyes restaurants subsequently sold out of the sandwich. Lines reached 45 minutes over the weekend in some places. Some towns may even nix the sandwich, because long Popeyes lines are contributing to traffic crashes.

One curious new customer, Chris Doyle, waited 20 minutes to get his hands on the scarce sandwich in Broomfield, Colorado. He lucked out. Popeyes stopped selling it minutes after he ordered.

The Chick-fil-A versus Popeyes debate on social media sparked our curiosity, Doyle said. I got both the classic and spicy sandwiches. I liked the classic better than the spicy, but both lived up to the hype. Every table was packed.

Longtime Popeyes franchisee Joseph Haberkorn Jr. said the social media froth is bringing record crowds to his Chicago restaurant.

Weve had lines out the door with guests clamoring for the new chicken sandwich, Haberkorn said. This weekend consisted of guests lining up all day, from open to close. In my 38 years as a Popeyes franchisee, Ive never seen a product create such a frenzy.

A viral sandwich. Unprecedented sales. The No. 1 trending topic on Twitter. By helping start this frenzy, did Chick-fil-A royally screw up?