A historic shift has gathered pace across Asia this summer.

Over the past several weeks, China has extended maritime patrols to cover Taiwan’s east coast, demonstrating its ability to encircle the island. It has intensified military, trade and diplomatic pressure on Japan and test-fired a submarine-launched ballistic missile that showcased its growing sea-based nuclear capability.

With an eye on China’s growing power, other countries have drawn closer, revealing the contours of an emerging new security architecture.

Japan has strengthened defense ties with Australia, the Philippines and India, and it is discussing closer cooperation with South Korea. Japan has also scrapped its longstanding restrictions on defense exports and is moving to join South Korea as a regional arms supplier, while Australia has signed new agreements with Pacific Island nations, including a mutual defense pact with Fiji.

Since President Trump’s return to office, uncertainty over his commitment to the defense of Asia has sparked warnings that Beijing could seize the opportunity to be more assertive, pushing U.S. allies to band together.

Those wheels are now turning, bringing new risks: Major changes in global security rarely unfold smoothly.

Yet this doesn’t have to mean we are entering an era of instability for an economically dynamic part of the world that remains vital to U.S. strategic interests. An order in which Asian countries assume greater responsibility for their own defense and rely more on one another — and less on an increasingly distracted United States — could ultimately prove stable and secure.

At any rate, it is unavoidable. An overextended United States is less prepared to underwrite Asia’s security indefinitely than it once was.

The war with Iran has exposed the limits of U.S. military power and prompted Washington to divert military assets from other parts of the world — including the Asia-Pacific region — and Mr. Trump has made clear that he wants U.S. allies to contribute more to their own defense. His administration has already announced significant reductions in the U.S. military presence and commitments in Europe. No comparable plans for Asia have emerged yet.

A transition to a more self-reliant Asia must be managed carefully.

If Beijing perceives a rapid weakening of American commitments or sees U.S. allies as newly vulnerable, it might conclude it has greater freedom to press its territorial and security ambitions, raising the specter of military confrontation.

Fear of that possibility, and of U.S. abandonment, could quicken the arms race already gripping East Asia. China has steadily built its armed forces and expanded its nuclear arsenal. Japan has recently begun deploying longer-range missiles, South Koreans are debating whether their country should develop its own nuclear weapons and Australia is investing in nuclear-powered submarines and missile capabilities.

Alarming as those developments sound, history has shown that Asian countries with diverse interests and forms of government can build working partnerships without deep U.S. participation. The 11-member Association of Southeast Asian Nations, founded in 1967, is often criticized as slow and indecisive in responding to shared challenges and has done little to counter China’s expansive territorial ambitions in the South China Sea. But ASEAN has helped to maintain peace among its members in a part of Asia previously torn by decades of war and provided a framework for Southeast Asia to engage with China.

A more balanced sharing of the security burden needn’t weaken deterrence. Deeper cooperation between countries such as Japan, the Philippines and Australia would actually strengthen the first line of defense against security threats, backed up by a gradually reduced — yet still robust — U.S. military presence.

As U.S. allies become more capable and integrated, it is only fair that they shoulder more of the costs of their own protection, freeing up thinly stretched American forces to meet global security challenges elsewhere. The United States, for its part, could continue to coordinate closely with its Asia-Pacific allies, take the lead on tasks central to U.S. interests, such as keeping vital sea lanes open, and work to maintain stable relations with China.

That kind of allied system would be stronger militarily, more durable over the long term than one that is overreliant on the United States and able to act collectively if American assistance is delayed or unavailable.

At any rate, the Middle East is proof that heavy American involvement is no guarantee that international rivalries won’t explode into conflict. The United States — along with Israel — started the war with Iran, exposing America’s partners in the Persian Gulf to Iranian attacks and disrupting global trade. As a result, some Gulf states are rethinking their reliance on Washington and exploring ways to maintain their security through partnerships among themselves, which may even include Iran.

The United States will remain a power in the Pacific. But the strategic balance has already shifted. American allies and rivals alike are wealthier and more capable than they were a generation ago, and U.S. forces are overstretched. Asia is adjusting to that new reality.