A Federal Trade Commission lawyer argued in court on Monday that Meta illegally monopolized the social media market, starting what is set to be a weekslong and high-stakes antitrust trial for one of the country’s largest tech companies.

Daniel Matheson, who is leading the FTC’s case against Meta, said during an opening statement at the federal courthouse in Washington, D.C., that U.S. policy has for more than a century “insisted firms must compete if they want to succeed” and that “Meta broke the deal.”