Apple posted some of its strongest growth during the March quarter in one of its toughest geographic regions.

The iPhone maker reported $13 billion in revenue from Greater China during its second fiscal quarter — a 21 percent year-over-year spike. That puts the company’s China revenue on par with its European revenue.

On the company’s earnings call, CEO Tim Cook said that the iPhone X, the company’s newest model, “was the most popular smartphone in all of China last quarter.”

The company’s performance in China is particularly impressive as overall smartphone sales were down in Q1, according to analysts at Canalys.

But Tim Cook wasn’t buying the bearish view of China.

“I don’t buy the view that the market’s saturated,” Cook said. “I think the smartphone market is sort of the best market for a consumer product company in the history of the world.”

China is one of Apple’s most important and competitive markets, and one that has increasingly been in the geopolitical spotlight amid trade tensions with the U.S.

Apple CEO Tim Cook visited the White House earlier this month, where he discussed Chinese tariffs and U.S. tax reform, according to Larry Kudlow, director of the National Economic Council.

Apple has faced increasing pressure to innovate as China’s domestic brands, like Huawei, Xiaomi and Oppo have gained popularity and moved toward higher-end handset specifications.

The company is one of the American companies most vulnerable to growing trade tensions between the U.S. and Chinese governments, with so much of its supply chain and revenue stream in China.

“My own view is that China and the U.S. have this unavoidable mutuality where China only wins if the U.S. wins and the U.S. only wins if China wins and the world only wins if China and the U.S. win,” Cook said on the earnings call. “I’m a big believer that the two countries together can both win and grow the pie, not just allocate it differently,” he said.

Apple also reported strong revenue growth in Japan, posting a 22 percent year-over-year jump. Revenue out of the Americas grew 17 percent; revenue in Europe grew 9 percent; and revenue in the rest of Asia Pacific grew 4 percent.