President Donald Trump aims to prevent conflict with China over Taiwan and the South China Sea by building up U.S. and allies’ military power, according to a new U.S. strategy memo.

The Trump administration laid out its approach to one of the world’s most sensitive diplomatic issues in an official, 29-page National Security Strategy document, dated November but only recently published online.

“Deterring a conflict over Taiwan, ideally by preserving military overmatch, is a priority,” according to the document.

China views democratically governed Taiwan as its own, and Beijing has never renounced the use of force to bring Taiwan under its control. China also has vast regional claims, including almost the entire South China Sea, which are disputed by many of its smaller neighbors.

The United States, like most countries, has no formal diplomatic ties with Taiwan. But Washington is the island’s most important international backer and is bound by law to provide Taiwan with the means to defend itself.

The Trump administration sees instability near Taiwan as a risk because of Taiwan’s dominance in semiconductor manufacturing and because a significant share of world trade passes through nearby waters, according to the document.

The issue has been an irritant in U.S.-China relations for years. Trump, a Republican, has largely avoided directly saying how he would respond to a rise in tensions over the island and said he is looking to maintain good ties with Chinese President Xi Jinping. He has also pressed Japan and South Korea, two key regional allies, to hike defense spending.

“We will build a military capable of denying aggression anywhere,” in the chain of islands stretching from Japan to Southeast Asia, according to the latest strategy document. “But the American military cannot, and should not have to, do this alone. Our allies must step up and spend -and more importantly do – much more for collective defense.”

That will reinforce “U.S. and allies’ capacity to deny any attempt to seize Taiwan” or any other steps that would “make defending that island impossible.”

The Trump administration also vowed to prevent “a potentially hostile power” from imposing a toll system or closing sea lanes. Doing so will require stronger naval capabilities, the document said.

It included a foreword signed by U.S. President Donald Trump, who said it was “a roadmap to ensure that America remains the greatest and most successful nation in human history.”

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(Reporting by Trevor Hunnicutt; editing by Philippa Fletcher)