Mark Zuckerberg defends Meta’s acquisitions of Instagram and WhatsApp on the first day of the antitrust trial.

Meta CEO Mark Zuckerberg took the stand Monday to defend his company against Federal Trade Commission (FTC) accusations that it acquired competing social media companies to gain market dominance with a monopoly.

It was the first of what is expected to be two days of testimony for Zuckerberg, who will seek to explain two of his company’s largest acquisitions, Instagram and WhatsApp.

And while Zuckerberg is no stranger to defending his company, the stakes in this case may be higher than ever. If the FTC wins, Meta could be forced to split up and divest WhatsApp and Instagram, disrupting the company’s core digital advertising business and reshaping the broader social media ecosystem.

Meta relies on the 3.3 billion daily users it claims to have on its platforms as one of the key selling points of its advertising business, which generated more than $160 billion in revenue last year alone.

But the government repeatedly argued in opening statements that Meta’s large user base reflected not simple success but a lack of choice, saying that “consumers have no reasonable alternatives” to Meta’s platforms. Meta’s lawyers argued that its platforms face a lot of competition in the social media space and that regulators approved the purchases years ago when they were made.

However, the FTC argued that the acquisitions were intended to prevent Meta from having to compete with potential upstart challengers by buying them instead. A 2011 email from Zuckerberg to Facebook executives detailed the company’s reasoning for buying Instagram, related to the company’s stalled efforts to develop an app called Facebook Camera.

“In the time it’s taken us to get this organized, Instagram has become a large and viable competitor to us in mobile photography, which will increasingly be the future of photography,” Zuckerberg wrote at the time. The company eventually acquired Instagram in April 2012.