Over the next decade, peace in the Indo-Pacific will largely hinge on whether the Chinese Communist Party (CCP) believes that the United States and its allies can stand in the way of a successful invasion of Taiwan. This growing threat has sparked significant debate about whether US policy toward Taiwan should become more explicit. In a recent Foreign Affairs article focused on Cold War lessons for the US-China competition, Hal Brands and John Lewis Gaddis observe that “the study of history is the best compass we have in navigating this future—even if it turns out to be not what we’d expected and not in most respects what we’ve experienced before.” In the case of Taiwan, however, disproportionate focus on the Cold War can obscure other historical cases that provide useful lessons for preventing geopolitical catastrophe.

One such instructive example is the United Kingdom’s commitment to preserving Belgian neutrality, which formed a consequential tenet of British foreign policy in the nineteenth and twentieth centuries. This case study provides important lessons for US-Taiwan relations today. For 75 years, London’s policy successfully deterred an invasion of Belgium before it failed in the opening days of the First World War. The United States is quickly approaching that same 75-year mark with Taiwan. The history of Britain’s commitment to Belgium illustrates that strategic clarity backed by diplomacy and strong military capabilities is more likely to deter great-power conflict and miscalculation than an undefined or ambiguous policy. As the United States navigates the Taiwan challenge, Washington should abandon strategic ambiguity, make an explicit commitment to defend Taiwan, and focus on building up the capabilities of the US and its allies to deter aggression by Beijing.

Trapped between Great Power Ambitions

In modern history, Belgium, a small yet strategically important state situated between France and Germany, exemplifies the challenge of deterring aggressive great powers. Under the Treaty of London (1839), the European powers—including Britain, France, and what was then the German Confederation—recognized the newly formed Belgian state and guaranteed its neutrality and independence. For the United Kingdom, however, this commitment was a key national interest. Given its pivotal location on the English Channel between France and the German states, a neutral Belgium would help prevent one power from gaining primacy on the European continent and forestall an invasion of the British Isles.

At the onset of the Franco-Prussian War (1870–71), the British commitment to Belgium faced its first major test when the country became a likely invasion route for the armies of both French Emperor Napoleon III and Prussian Chancellor Otto von Bismarck. Dispatches in the Foreign Office papers indicate that Britain’s ambassadors in Paris and Berlin quickly received assurances that neither power would violate their treaty commitment to Belgium’s neutrality. Subsequently, it became public in the Times of Londonthat a few years earlier, Count Benedetti, the French ambassador to Prussia, had discussed a draft treaty with Bismarck that included a proposal to have France annex Belgium, which would directly repudiate the commitment of both powers to the 1839 treaty.

The revelation of the Benedetti Draft Treaty created an immediate crisis in London. Prime Minister William Gladstone and his foreign secretary, Earl Granville, faced questions from Parliament about the security of Belgium amid the impending war. In response to the controversy, Gladstone informed Queen Victoria that the British Cabinet resolved to pursue a policy that combined diplomatic arrangements and military preparations. Granville convinced France and Prussia to each agree to identical, bilateral treaties for the duration of the conflict that would reaffirm Belgian neutrality and commit the United Kingdom to join with either side to defend Belgium if the other power reneged on its commitment. The British government also successfully lobbied Parliament to increase funding for the armed forces and add 20,000 troops to the British army for the purpose of defending Belgium if necessary.

The treaties British leaders quickly concluded with both France and Prussia in 1870 amounted to a significant achievement by the preeminent global power of the time. While the European powers widely believed that Britain would respond to a violation of Belgian neutrality, the new agreements represented a rare instance of an explicit British treaty obligation to intervene militarily if its interests were threatened.

In contrast with Gladstone’s diplomatic efforts during the Franco-Prussian War, on the eve of the First World War the British Cabinet did not decide to support Belgium against an invasion until two days before Britain declared war on Imperial Germany. As Christopher Clark writes in The Sleepwalkers: How Europe Went to War in 1914, there was “nothing automatic about the relationship between a German invasion of Belgium and British intervention in the conflict.” Consequently, Britain did not attempt to use the threat of intervention to preserve Belgian neutrality. A key constraint on British policy was long-running Imperial German war plans that depended on Belgium to outflank French forces, effectively pitting efforts to deter a threat to Belgium against the inertia of Germany’s war machine once Berlin began mobilizing its forces. Additionally, Britain had other motivations beyond Belgium to enter the conflict engulfing the European continent, most notably the potential consequences for its imperial holdings of being left out of a future post-war settlement.

Even considering these complications, comparing the results of British policy in both conflicts is striking. In September 1870, Napoleon III chose to surrender his entire army to the Prussians at Sedan rather than cross the Belgian border to escape capture, which might have provoked a British intervention in the conflict. Meanwhile, as Clark recounts, Kaiser Wilhelm II’s generals fatefully “did not attach great importance to the question of British intervention” in 1914. Given this thinking, Germany calculated that the risk of drawing Britain into the war was worth the military benefits of violating Belgium’s neutrality. It is impossible to know if the failure of British leaders to pursue a clear deterrence strategy for such an important security interest would have fundamentally altered the history of the war. But while deterrence does not always succeed, ambiguity surrounding Britain’s red line in Belgium and the consequences of crossing it undermined efforts to reduce the risk of aggression.

The Path Forward

The animating principle of US strategy in the Indo-Pacific—which has long centered on preventing the emergence of a regional hegemon that can threaten the interests of the United States and its allies—would not have been unfamiliar to nineteenth and twentieth-century British leaders. Taiwan is located in a strategically important hinge point in the first island chain. It abuts a key shipping lane linking the East China Sea and South China Sea and has maintained close ties with the United States for decades. Despite these interests, the threat posed by the CCP’s claim to the island, and Taipei’s now-flourishing democracy, there is no explicit American commitment to deter an unprovoked attack on the island. Current US policy strongly infers that an invasion or economic coercion campaign against Taiwan would be met with a forceful American response. But this policy, as laid out in the Taiwan Relations Act, revolves around strategic ambiguity in saying only that the United States “consider[s] any effort to determine the future of Taiwan by other than peaceful means, including by boycotts or embargoes, a threat to the peace and security of the Western Pacific area and of grave concern to the United States” [emphasis added].

As US policymakers weigh the merits of the current US posture toward Taiwan, they should recall the lessons of Britain’s Belgium policy and the challenges of pursuing an ambiguous deterrence strategy. US strategic ambiguity on Taiwan might have been sufficient when the People’s Republic of China (PRC) was not a near-peer military competitor, but it no longer meets the moment. As Beijing violates its citizens’ human rights including religious liberty, the People’s Liberation Army continues to bolster its capabilities with an eye toward denying the United States the ability to stop an invasion of Taiwan, and that threat is no longer hypothetical. With senior CCP leaders believing that the United States is in decline, strategic clarity backed up by credible capabilities is now essential for deterrence. And the audience for US policy is not just Beijing. America’s Indo-Pacific allies should know how the United States will respond in a crisis and have confidence that the United States can back up its commitments.

Critics of abandoning strategic ambiguity have made important arguments that deserve consideration. Notably, the current approach has had an important role in balancing the US “One China” policy with maintaining security ties to Taiwan. But many commentators have outlined how the United States can avoid violating the “One China” policy or needlessly provoking the PRC, which includes ensuring that US policy remains detached from a unilateral Taiwanese declaration of independence. Critics also argue that an explicit US commitment could make a pre-emptive Chinese strike against US forces more likely or cause US allies to fear that the United States will drag them into a war. While both arguments raise realistic possibilities, most countries in the region, including the PRC, already largely assume the United States would mount at least some kind of military response to an invasion of Taiwan. Putting aside the debate over strategic or tactical ambiguity in US policy, however, the United States certainly needs clarity on its goals with regard to Taiwan, as Jianli Yang argues in these pages.

In addition to diplomacy, strategic clarity cannot succeed without a concerted focus on building and maintaining US military strength to deter the PRC credibly in the Indo-Pacific. Growing domestic political support provides critical backing for these efforts. Despite the narrative that declining public support for US involvement in Afghanistan translated into broader support for US retrenchment worldwide, a recent Chicago Council on Global Affairs poll found that 52 percent of Americans would support deploying US troops if the PRC invaded Taiwan, an 11 percent increase from 2020. Congress should seize on this momentum and give the president the ability to follow through on a stronger commitment to Taiwan, including legal authorities, additional support for military priorities such as the Pacific Deterrence Initiative, and efforts to deepen bilateral ties with Taiwan.

As the PRC escalates its menacing of Taiwan, it is time to move past the question of whether the United States will act. Instead, Washington should focus on how it will work with Taiwan and other allies and partners to deter Beijing from the full range of actions that could imperil Taipei’s security. In the process, the American national security community would be wise to look to history—including the record of Britain’s policy toward Belgium—to inform US policy.