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

As the government wraps up its case, it has built a picture of how Google has become dominant among companies that buy and sell ads online.

The Justice Department accuses the Silicon Valley tech firm of engaging in a systematic campaign to seize control of high-tech tools used by publishers, advertisers and brokers to facilitate digital advertising.