WASHINGTON (AP) -- Meta CEO Mark Zuckerberg emphasized in federal court on Wednesday that he bought Instagram and WhatsApp because he saw value in the companies -- not to take out competitors, as the Federal Trade Commission alleges in a historic antitrust trial.

Zuckerberg took the stand for the third day in the trial, wrapping up his testimony as the first witness Wednesday afternoon. He took questions from Meta attorney Mark Hansen, who has argued that his client hardly has a monopoly in social media, as the FTC claims, and still faces stiff global competition.

Hansen focused some of his questioning on emails sent by Zuckerberg and his associates that the FTC cited in earlier testimony to illustrate the Facebook founder's alarm over the growth of Instagram and his sense that he needed to neutralize its threat.

Zuckerberg said he's very focused on inventing new things, and understanding what other people are creating is a big part of the process. At any given point in his company's history, he said, similar tones of concern could be found in emails about what other companies were doing better than his.

"This is my job," Zuckerberg said. "I need to understand what is going on, and I need to push our teams to move quickly" to learn about what is going on in a very competitive market.

Hansen questioned Zuckerberg about competition, particularly from TikTok, the popular social media site owned by Beijing-based company ByteDance, and the the growth of the video-sharing platform YouTube, which is owned by Alphabet.

Zuckerberg testified that people spend more time on YouTube than on Facebook and Instagram combined.

While Hansen noted that the FTC doesn't consider YouTube to be a Meta competitor -- because it doesn't have the same friend-sharing technology as Facebook -- Zuckerberg said YouTube has built in ways to share videos.

The FTC contends Meta has used a monopoly in its technology that facilitates connecting with friends and family to generate enormous profits as consumer satisfaction has dropped. The case could force the tech giant to break off Instagram and WhatsApp, startups it bought more than a decade ago that have since grown into social media powerhouses.

Daniel Matheson, the FTC's attorney who questioned Zuckerberg, has repeatedly brought up his own words in emails to associates before and after the acquisition of Instagram to try to show Zuckerberg was more interested halting Instagram's alarming growth than improving the product.

Under questioning by Hansen, Zuckerberg insisted that he had no intention of acquiring Instagram only to slow its development and end a threat. He said the focus was on "having it run as an independent brand."

Hansen noted that the FTC is making similar claims about the acquisition of the messaging app WhatsApp: that Zuckerberg was afraid of the company's potential.

"It's something I thought about," Zuckerberg said, noting the app's formidable capabilities, but he added that he later learned not to be worried because the owners didn't share the same vision or direction.

He said his interest in buying it was "the usage of it."

"I thought the app was important and valuable," Zuckerberg said.

The trial, which is slated to last weeks, will feature other Big-Tech figures. After Zuckerberg, Sheryl Sandberg, Facebook's former chief operating officer, took the stand.

The trial is one of the first big tests of President Donald Trump's FTC's ability to challenge Big Tech. The lawsuit was filed against Meta -- then called Facebook -- in 2020, during Trump's first term. It claims the company bought Instagram and WhatsApp to squash competition and establish an illegal monopoly in the social media market.

Facebook bought Instagram -- which was a photo-sharing app with no ads -- for $1 billion in 2012.

Instagram was the first company Facebook bought and kept running as a separate app. Until then, Facebook was known for smaller "acqui-hires" -- a popular Silicon Valley deal in which a company purchases a startup as a way to hire its talented workers, then shuts the acquired company down. Two years later, it did it again with the messaging app WhatsApp, which it purchased for $22 billion.

WhatsApp and Instagram helped Facebook move its business from desktop computers to mobile devices, and to remain popular with younger generations as rivals like Snapchat (which it also tried, but failed, to buy) and TikTok emerged.

U.S. District Judge James Boasberg is presiding over the case. Late last year, he denied Meta's request for a summary judgment and ruled that the case must go to trial.