Netflix, Amazon and Hulu have suddenly found themselves playing a new role: the establishment.

After years of waging an assault on the traditional television business, these companies now must defend their turf on the battleground of the future, Internet streaming. HBO, Apple, Sony, Dish and other companies that were once challenged by services like Netflix have stormed onto the field in recent weeks, making a splash with new streaming offerings and bold pronouncements on reinventing the way people watch and pay for television.

Those advances have raised the stakes for Netflix, Amazon and Hulu, which not only invented the category but also induced a wave of TV fans to watch their favorite programs without paying for a cable or satellite subscription. Now, new competition is forcing those companies to invest even more in exclusive, original productions, innovate their technologies, explore new partnerships and ramp up their marketing.

“In a world where HBO and CBS and all of these guys are trying to go to the Internet, it looks like all of the guys on the Internet are trying to come to the television,” said Kannan Venkateshwar, a media analyst at Barclays. “The worlds are actually converging in both directions.”