Google has opened its defense against allegations that it holds an illegal monopoly on online advertising technology with witness testimony saying the industry is vastly more complex and competitive than portrayed by the federal government.

If the DoJ's lawsuit fails, the online ecosystem could worsen for users and third-party companies. Lawyers, nonprofit organizations, and privacy experts recently held a press hearing

The US government has accused Google of manipulating the ad tech market, stifling competition and innovation; the company recently lost an antitrust case targeting its search business.

The Justice Department and multiple states allege that Google holds a monopoly over online advertising technology, shutting out competitors and charging high fees. Google counters that the government is focusing too narrowly on specific types of ads.

Google has monopolized the technology used to buy and sell online display ads by restricting or eliminating the choices of its customers — both website publishers and advertisers — the US Justice Department alleged at a federal antitrust trial.

The judge who will decide whether Google holds a monopoly over technology that matches buyers and sellers of online advertising must choose whether to believe what Google executives wrote or what they have said on the witness stand.