For the more than three decades since the United States’ recognition of the People’s Republic of China, Washington has relied on strategic ambiguity to deter China from using force against Taiwan. Although the Taiwan Relations Act of 1979, passed by Congress after U.S. President Jimmy Carter established diplomatic relations with Beijing, calls for the U.S. to help Taiwan defend itself, in application the U.S. has often kept the two sides guessing at its willingness to intervene in a conflict, and if so, in what capacity.

Such ambiguity worked for three decades, but it won’t last for much longer.

As long as the People’s Liberation Army (PLA) remained the weaker party in the trilateral relationship, ambiguity was sufficient to deter China from launching an attack on Taiwan. With China’s emergence as an economic powerhouse, and its concurrent military buildup, that ambiguity has not only lost its effectiveness — it is now an invitation for adventurism.

The détente in the Taiwan Strait following the election of Taiwanese President Ma Ying-jeou in 2008, added to China’s increasingly aggressive behavior in the South China Sea, has convinced some observers that Beijing has shifted its military away from the Taiwan Strait and is now concentrating on other regional contingencies. However, in reality, Taiwan remains Beijing’s top core interest, and its leadership is fully aware that while relations with Taipei are currently moving in China’s favor, the situation could change quickly and might require the application of force to bring about Beijing’s ultimate goal of unification. Less than two months since Ma began his second — and last — term, political negotiations between the two sides remain infeasible. Taipei made that very clear late last month when it denied Chinese academics visas so they could attend a conference on political dialogue in Taipei.

Domestic requirements being what they are, Ma was forced to make it clear during his first term that he intended only to tackle the “easy” aspects of the relationship, such as economic liberalization, first, and address political issues later, when and if the conditions were propitious. That time might never come; as one report notes, “less than 10 percent of respondents (in a recent poll) supported unification with China, suggesting that more than 90 percent of Taiwanese do not support unification.”

With their decision to re-elect Ma, Taiwanese signaled that while they support the long-delayed — and necessary — liberalization of relations across the Taiwan Strait, they also do not regard themselves as Chinese, and have no intention of being absorbed by their neighbor, especially one that remains undemocratic and repressive.

The question, therefore, is what Beijing will do when it realizes that growing economic interaction will not translate into support for unification. Coercion, or use of force, could then become more appealing to the Chinese Communist Party, especially if it believes it can do so at a relatively low cost — in other words, if it is convinced that the U.S. will not intervene.

A lot of publicity has surrounded the ongoing U.S. strategic “pivot” to Asia, which for the most part many would argue was prompted by developments in the South China Sea and calls by some of the claimants, principally the Philippines and Vietnam, for U.S. assistance in countering a resurgent China. Publicly, while Washington has re-emphasized its engagement with allies in the region, from Japan to Australia, in most instances Washington has omitted mentioning Taiwan as a regional partner. This was ostensibly to avoid undermining warming ties between Taipei and Beijing.

A number of factors, however, cast serious doubts on the wisdom of excluding Taiwan from the “pivot.”

Among them is the fact that Beijing may be using the South China Sea disputes, which it can wage at relatively low cost by relying mostly on maritime surveillance ships and fishing vessels, as a distraction or a sideshow, while continuing to build up its military forces facing Taiwan. Were the U.S. to reorient its military predominantly for the purposes of addressing a South China Sea contingency (e.g. by favoring deployments in Southeast Asia or as far south as Australia), it could find itself unprepared, if not unable, to deal with an attack on Taiwan.

Through its belligerence in the South China Sea — an area whose importance is only secondary to its goal of unification with Taiwan — China has also repeatedly and unapologetically displayed its fixation on “history,” often at the expense of international law or multilateral approaches to conflict resolution. While this intransigence bodes ill for the possibility of resolving sovereignty disputes in the South China Sea, it portends even more ominously for China’s approach to political negotiations with Taiwan, which in turn could make the military option more likely at some point in the future.

The best way to avoid war over Taiwan and to ensure that U.S. forces are not wrong-footed should such a scenario unfold, therefore, is for Washington to put an end to its strategic ambiguity and to clearly state that it will defend Taiwan should China threaten force against it. By doing so, the U.S. would not only ensure that Beijing does not miscalculate by believing it can use the military option on the cheap — thereby lowering the probability of armed conflict — it would also provide Taipei with the backing it needs to negotiate with Beijing as an equal rather than a weaker party coerced into making political concessions against the wishes of its population.

The responsibility does not lie with the U.S. alone, however. Taiwan must also demonstrate that it is committed to defending itself and to assuming its role as an ally of the U.S. in Asia. Among other things, this calls for meeting the goal of allocating at least 3 percent of GDP for the national defense budget and making sure that an ongoing program to create an all-volunteer military by 2015 is handled properly and given sufficient funding, which for the moment remains in doubt. U.S.-Taiwan military cooperation, though generally kept away from public view, remains healthy, but much more can be done at the political level to signal that the relationship is durable and mutually beneficial. In other words, Taiwan may also have to abandon the ambiguous language the Ma administration has used in recent years to facilitate rapprochement with China.

Simply stated: The usefulness of ambiguity has passed.

While the Obama administration, breaking the precedent set by previous administrations, took a conciliatory approach to China when it entered office, it has since realized that Beijing does not intend to play by the rules and remains, despite wishes to the contrary, an irresponsible stakeholder on several important issues.

War over Taiwan is not inevitable, but signs of weakness or disinterest on Washington’s part could make that option more attractive to Beijing, especially when its efforts to achieve unification by “peaceful” means run into difficulties, as they most certainly will.