When China launched threatening war games off Taiwan 15 years ago on the eve of an election on the self-governing island, the U.S. deployed two aircraft carriers, and China quickly backed down.
Things do not seem so one-sided any more.
China's military has been on a spending spree at a time that the debt-ridden U.S. government is looking to cut defense costs. Last week, China announced a 12.7 percent increase for this year, the latest in a string of double-digit increases.
That trend has triggered worries in Congress and among security analysts about whether the United States can maintain its decades-long military predominance in the economically crucial Asia-Pacific region.
While the U.S. military has been drained by 10 years of costly conflicts in Afghanistan and Iraq, China has developed air, naval and missile capabilities that could undercut U.S. superiority in China's backyard.
China is still decades away from building a military as strong as the United States. It has not fought a major conflict since a border war with Vietnam in 1979 and is not a Soviet-style rival threatening American soil.
However, the shift raises questions about whether the United States can meet its commitment to maintaining a strong presence in the Asia-Pacific for decades to project global power, safeguard shipping lanes vital for world trade and protect regional allies.
China already has an innate geographical advantage in any conflict in the western Pacific. One expert speculated that, with its military buildup, China could conquer Taiwan by the end of the decade, even if the U.S. military intervened.
China regards Taiwan as part of its territory. Relations between the two, long seen as a potential flash point, have warmed in the past two years.
But China's assertion of territorial claims in the South China Sea has spooked its neighbors and fortified their support for a strong U.S. presence in the region. Even former enemy Vietnam is forging military ties with the United States.
Last week, the Philippines deployed two warplanes after a ship searching for oil complained it was harassed by two Chinese patrol boats in the South China Sea. Japan scrambled F-15 fighter jets after Chinese surveillance and anti-submarine aircraft flew near disputed islands in the East China Sea.
"As China's military has gotten more capable, and China has behaved more aggressively, a number of countries are looking at the U.S. as a hedge to make sure they can maintain independence, security and stability," said Abraham Denmark, director of the Asia-Pacific Security Program at the Center for a New American Security.
But those allies question whether the United States can retain its freedom to operate in the region, and whether its economy - highly indebted to China and struggling to recover from a recession - can sustain its high level of military spending, said Bonnie Glaser of the Center of Strategic and International Studies.
The U.S. Pacific Command has 325,000 personnel, five aircraft-carrier strike groups, 180 ships and nearly 2,000 aircraft. Tens of thousands of forces stay on China's doorstep at long-established bases in South Korea and Japan.
China's defense spending is still dwarfed by the United States. Even if China really invests twice as much in its military as its official $91.5 billion budget, that would still be only about a quarter of U.S. spending. It has no aircraft carriers and lags the United States in defense technology. Some of its most vaunted recent military advances will take years to reach operation.
For example, China test-flew its stealth fighter in January, months earlier than U.S. intelligence expected, but U.S. Defense Secretary Robert M. Gates says China will still only have a couple of hundred of these "fifth-generation" jets by 2025. The United States should have 1,500 by then.
China's growing array of aircraft, naval and submarine vessels, ballistic and cruise missiles, anti-satellite and cyberwar capabilities already enable it to project power beyond its shores. It plans new submarines, larger naval destroyers and transport aircraft that could expand that reach further.
Roger Cliff, a respected defense researcher who recently testified before a congressional hearing on China, said many of the missiles and strike aircraft have a range of about 900 miles, which put them within attacking distance of virtually all U.S. air and naval bases in the region.
They include the DF-21D missile, which is designed to target aircraft carriers. It employs technology that no other U.S. rival has mastered.
Mr. Cliff said if trends continue, China should have sufficient missiles and precision bombs by the end of the decade to render inoperable for a week or more all airfields on Taiwan and U.S. air bases in Okinawa, Japan, and possibly others farther away.
He said China has between 40 and 50 air bases within 500 miles of Taiwan, each generally hosting a squadron of 24 aircraft, which could overwhelm superior U.S. aircraft through sheer numbers. If China acquired amphibious landing vehicles, he forecast it could conquer Taiwan.
If U.S. military planners are worried about that possibility, they are not showing it. They say plans to cap defense spending within five years will not derail modernization plans. Pacific Command chief Adm. Robert Willard said last month that, while the United States carefully watches China's growing military capabilities - and urges greater openness from China about them - the United States does not need to change its strategy.
China maintains it does not have offensive intentions, and analysts say that military action in the region would hurt its export-driven economy, which could threaten what its government prizes above all else - domestic stability. The U.S. military presence also may benefit China as it restrains neighbors like South Korea and Japan from seeking nuclear weapons.
As U.S. and Chinese forces increasingly rub up against each other in the western Pacific, the United States says it wants to promote military ties with China to prevent a chance skirmish and for China to develop as a "responsible major power." To date, China has been reluctant to engage meaningfully after the recent restoration of military ties that were cut over U.S. arms sales to Taiwan.
"This is not the Cold War with two rival camps facing each other," said Michael Schiffer, U.S. deputy assistant secretary of defense for East Asia. "We are seeking a military-to-military relationship that is broad and deep enough to manage our differences while expanding on areas of common interest."