Cases around Google and Facebook, two companies with clear dominance in their markets of search, social media and online advertising, took shape faster than the other companies. Google had been the subject of a search antitrust investigation that closed at the F.T.C. in 2013 without a lawsuit but created a trove of information. Facebook’s case quickly coalesced around its prior mergers, which regulators were able to investigate because of its past investigations into those acquisitions, some people close to the investigations said.
The F.T.C. was split on its decision to pursue the lawsuit, with its chairman, Joseph Simons, a Republican appointed by Mr. Trump, and the two Democratic commissioners joined in their vote. The two remaining Republican commissioners voted against the lawsuit.
The state suit was signed by attorneys general from 46 states and the District of Columbia and Guam. Georgia, South Dakota, Alabama and South Carolina did not join the case.
There is a history of states going after large tech companies. In the landmark antitrust suit against Microsoft two decades ago, state attorneys general played a crucial role in pushing the case through years of litigation.
Several Facebook rivals, including Snap, came forward to present evidence of what they said was anticompetitive behavior. Mr. Zuckerberg was interviewed for the federal investigation, and prosecutors collected many of his communications to Facebook employees, investors and the leaders of the rivals he bought and tried to buy.
In a hearing before the House judiciary committee last July, Mr. Zuckerberg was confronted with emails from around the time of the acquisition of Instagram and WhatsApp that showed the Facebook’s founder saw the companies as competition and potentially a threat. Mr. Zuckerberg said the acquisitions have not reduced competition and that the emails were taken out of context.
The agency and states said the purchases ended up giving Facebook data on users that fed into its business of behavioral advertising, buttressing its monopoly.
“Facebook has coupled its acquisition strategy with exclusionary tactics that snuffed out competitive threats,” the states said in their suit, “and sent the message to technology firms that, in the words of one participant, if you stepped into Facebook’s turf or resisted pressure to sell, Zuckerberg would go into ‘destroy mode,’ subjecting your business to the ‘wrath of Mark.’ ”
