Unless you’ve been living under a rock, you’ve probably heard of Fortnite: Battle Royale, the video game that’s taken the world by storm.

Here’s how it works: You and 99 other players are dropped out of a flying bus (not a typo) onto an island. You land with nothing but your wits and a pickax. As the game starts, there’s usually space between you and the next person, which gives you time to scrounge up supplies and weapons — and use your pickax to take apart walls, furniture and anything else you can find nearby. As the game goes on, the landscape effectively shrinks, forcing players closer together and into combat. It’s them or you — so everyone starts to pick each other off, Hunger Games-style, until there’s a winner.

Fortnite wasn’t the first to use this addictive formula called “battle royale” inside the video game industry, but its quirky take helped turn the game into one of the biggest hits in years. On Tuesday, Fortnite maker Epic Games said during the E3 Electronic Entertainment Expo in Los Angeles that 125 million people have played Fortnite since it was released for PCs, Macs, the PlayStation 4, the Xbox One and mobile devices beginning nearly a year ago.

And though the game is a free download, in the month of April alone Epic rang up nearly $300 million in sales of add-ons such as color schemes for weapons or new outfits for characters, according to industry watcher SuperData Research. Fortnite also sells dance moves for characters, called “emotes,” that have become so popular that real-life sports stars including Cleveland Browns quarterback Baker Mayfield have taken to re-enacting them in real life (and Fortnite, has taken inspiration from stars like the MMA champ Conor McGregor.)

So it’s probably no surprise that Activision last month said its rival war simulation game, Call of Duty: Black Ops 4, will also have a battle royale mode when it comes out later this year. And on Saturday, Electronic Arts said it will offer a battle royale mode for its upcoming WW II-themed Battlefield 5 game, after fans asked it to take on the genre.

“The raw gameplay is what draws people into it, which is brilliant,” said Patrick Söderlund, EA’s head of design. “That’s how a game should be.”

Battle royale is popular for a reason. It’s the latest example of how many of the games we play are changing dramatically to focus on people playing together rather than one person playing alone. Thanks to the internet and powerful services such as Xbox Live and PlayStation Plus, game makers are tapping into our primal urges to compete against one another, giving us all manner of new ways to play.

The Hunger Games approach caught on thanks to the drama that comes with it. The shrinking circle of play, the defined winner and how everyone’s pitted against one another makes the game not just fun to play, but entertaining to watch too. Which is part of the reason why Fortnite is the top game on the streaming service Twitch.TV. (PlayerUnknowns Battlegrounds, its next largest competitor, is currently ranked seventh-most streamed.)

Epic is looking to take advantage of that popularity with a big push into esports, announcing Wednesday the first Fortnite World Cup will be held in 2019 with qualifiers taking place later this year. The company said it will drop $100,000,000 to fund prize pools for Fortnite competitions.

Frank Azor, head of Dell’s Alienware gaming PC division, said his 6- and 8-year-old kids began playing Fortnite after talking about it with friends at school and watching videos of people mimicking the celebratory dances online. Before Fortnite, they’d played the world-building game Roblox and Blizzard’s cartoonish superhero shooter Overwatch. But now, it’s all about Fortnite.

And he doesn’t think they’re alone. Sales of Alienware’s powerful PCs have jumped double digits this year, he says, something he attributes in part to Fortnite.

“It’s crossing into the mainstream,” Azor said of the game.