Enlarge / A staffer with the Paul, Weiss legal firm wheels boxes of legal documents into the Albert V. Bryan US Courthouse at the start of a Department of Justice antitrust trial against Google over its advertiing business in Alexandria, Virginia, on September 9, 2024. Google faces its second major antitrust trial in less than a year, with the US government accusing the tech giant of dominating online advertising and stifling competition. (credit: SAMUEL CORUM / Contributor | AFP)

Just a couple of days into the Google ad tech antitrust trial, it seems clear that the heart of the US Department of Justice's case is proving that Google Ad Manager is the key to the tech giant's alleged monopoly.

Google Ad Manager is the buy-and-sell side ad tech platform launched following Google's acquisition of DoubleClick and AdX in 2008 for $3 billion. It is currently used to connect Google's publisher ad servers with its ad exchanges, tying the two together in a way that allegedly locks the majority of publishers into paying higher fees on the publisher side because they can't afford to drop Google's ad exchange.

The DOJ has argued that Google Ad Manager "serves 90 percent of publishers that use the ad tech tools to sell their online ad inventory," AdAge reported, and through it, Google clearly wields monopoly powers.