The United States military hasn’t conducted a single combat operation within the sprawling area of responsibility ^[1] that defines the Indo-Pacific Command (INDOPACOM) in 44 years. I’m overly fond of pointing out this little-commented-on fact of Indo-Pacific security, because its significance is underappreciated.

The last US combat operation ^[2] in the region was in Cambodia, in May 1975, against the newly victorious Khmer Rouge, which had recently captured an American-flagged merchant ship, the SS Mayaguez. The forceful US response was a spasmodic demonstration of resolve: a coda to Washington’s humiliating abandonment of South Vietnam and precursor to a more ‘offshore’, less interventionist Pacific posture.

Since then, US forces haven’t engaged in combat anywhere in the western Pacific, in spite of many crises and reactive deployments to the region’s numerous flashpoints, such as the Taiwan Strait, the Korean peninsula and the South China Sea. Afghanistan falls within the area of responsibility of US Central Command (CENTCOM).

This situation held throughout the so-called unipolar moment, including the post-9/11 high-water mark of US global military activism, when Southeast Asia was labelled as a second front in the ‘war on terror’. US forces provided non-combat counterterrorism support to Philippine forces, but exercised greater restraint than in other US combatant commands ^[3].

In fact, US forces have seen more recent action in Europe than they have in the Indo-Pacific. The 2011 special forces raid on Osama bin Laden’s compound, at Abbottabad in Pakistan, fell technically within PACOM’s area of responsibility. But that was a sui generis spillover from CENTCOM.

Empirically, the absence of armed intervention appears at odds with Asia’s persistent security crises, nationalist fault lines and substantial investments in modern military power. The contrast sharpens after factoring in that America’s bloodiest post-1945 military interventions were in Korea and Vietnam.

A reasonable conclusion might be that deterrence has successfully maintained the peace in Asia, especially East Asia, underpinned by US forward-deployed combat forces and intelligence-gathering capabilities. The US presence bought time for post-colonial states to achieve internal stability, while deterring external adventurism and providing sufficient forewarning of hostile intentions so that crises could be contained below boiling point.

But that sounded much more convincing 10 years ago than it does today. In the intervening decade, North Korea has sunk ^[4] a South Korean warship, shelled South Korean civilians and gatecrashed into the thermonuclear intercontinental ballistic missile club—all without incurring a single retaliatory US shot.

In the South China Sea, the US stood by as China transformed disputed specks into artificial bases that today support military and paramilitary forward operations, incrementally intimidating Southeast Asian states into submission. In 2012, the US didn’t intervene when China wrested control over the Scarborough Shoal ^[5] from the Philippines, another US treaty ally.

Today, Vietnam appears isolated within ASEAN, as a lone source of resistance to China’s ongoing encroachments in the South China Sea. US freedom-of-navigation operations ^[6] have done nothing to reverse this creeping expansionism, although belated US deterrent signalling ^[7] appeared to dissuade China from constructing another artificial island base at Scarborough Shoal.

We tend to think of China’s ‘grey zone’ tactics in the South and East China Seas, and North Korea’s asymmetric provocations as somehow novel. But China ^[8] and North Korea ^[9] are both seasoned exponents of hybrid warfare. What has changed is the intensity and sophistication of such tactics, which are now reaping strategic effects.

US abstention from using force in the western Pacific undoubtedly owes something to successful deterrence. Far less widely understood is that the threshold for using armed force in Asia is higher than in most other regions. The existence of nuclear weapons in South and Northeast Asia is one factor in this, but not the whole explanation.

The India–Pakistan strategic dynamic is perhaps an outlier in this respect, underlined by the Balakot airstrike ^[10] and aerial encounters that took place earlier this year. North and South Korea have also traded blows, despite the existence of nuclear weapons on the peninsula. One big difference, however, is that US credibility is directly on the line in East Asia—combat forces are present in Japan and South Korea, and Washington’s extended nuclear deterrence guarantees apply to Seoul, Tokyo and Canberra.

In reality, the US military has trodden, flown and swum rather carefully in the western Pacific since the Vietnam War, not only because peace has largely prevailed but because the risks of war with North Korea and China are perceived to be very high.

This forbearance is essential to understanding why INDOPACOM’s area of responsibility hasn’t experienced a single US combat operation in nearly half a century. Imagine North Korea relocated to North Africa and China’s South China Sea artificial bases transposed to the Persian Gulf, and see if you get the same results.

It flows from this that military entrapment is overestimated as a strategic risk among US treaty allies and close partners in Asia, and abandonment is probably underestimated. While it would be unwise to underestimate the resolve of the US, particularly if its armed forces, territory or citizens were directly attacked, the historical record suggests that the bar for US military intervention in the Indo-Pacific region is significantly higher than many observers think, even in defence of allies.

Don’t get me wrong: I’m not urging the US to undertake another Mayaguez operation in order to reassure jittery allies and deliver a slice of shock and awe to deter emboldened adversaries in the region. The US military has amassed plenty of combat experience elsewhere in recent decades. Too much of the wrong kind, perhaps, but it still counts in the mix.

By the same token, it’s worth remembering that China has more recent experience of fighting a conventional war in East Asia than America. Given this, it’s fortunate that no country in the region has a particularly fond memory of its most recent war—not China, not Japan, not the Koreas, and not Vietnam ^[11].

If that has helped to raise the threshold for war, it also lends a symbolic, demonstrative aspect to the next state-on-state conflict. Wherever and however it breaks out, everyone will be watching, and it will be more important than ever not to end up as the losing side. Once the Rubicon of armed combat has been crossed, even inadvertently, substantial escalatory pressures could come into play from leaders unwilling to wear the political consequences of defeat. One particularly thinks of China in this regard.

Arguably, the absence of recent combat experience in the region will reinforce caution among the region’s revisionist powers and a preference for challenging the status quo below the threshold of armed conflict. However, the strategic pickings available from grey-zone tactics are growing thinner, now that the US and regional countries are latterly waking up to the fact that warfare was never permanently banished from the region. It just took on other guises.