Of all the questions raised by the U.S. campaign against the Islamic State of Iraq and al-Sham (ISIS), one is particularly contentious: Does the United States have the legal authority to extend airstrikes from Iraq to Syria? Although its current air campaign is legal -- Iraq has formally asked the United States and coalition forces to aid in the fight against ISIS -- Syria has neither sought assistance nor given consent for foreign countries to launch attacks within its territory.

In recent hearings, U.S. Secretary of State John Kerry defended a possible foray into Syria by repurposing an old concept from international law: the right of hot pursuit. The doctrine has traditionally applied to the right of a navy to chase pirate ships from its territorial waters into the high seas. And in its modern incarnation -- as part of domestic criminal law -- the doctrine is primarily used to allow law enforcement officials to pursue criminals fleeing across borders.

But whether the United States could invoke hot pursuit to chase militants into Syria is a different question altogether. The answer risks putting U.S. policymakers on a dangerous slippery slope. If history is any guide, by invoking the term, Washington could be opening a Pandora’s box of political ironies and potential legal dilemmas.


In recent decades, countries from Brazil to South Africa have used the term “hot pursuit” with gusto. And every instance hints at possible ways in which the concept could be misused or exploited for political gain.

First, countries that invoke the right of hot pursuit often exaggerate the threat posed by nonstate actors in order to garner international sympathy and dilute criticism of their aggression. One case in point is South Africa’s use of the term to justify frequent raids into Angola in the 1970s. The ostensible goal of these incursions was to target separatists from the South West Africa People's Organization, a group fighting for the independence of Namibia, which was then under South Africa’s control. But South Africa also had a different strategic objective altogether: supporting the guerrilla leader Jonas Savimbi, who sought to topple the Angolan government. 

The phrase “hot pursuit” has also often served as a rhetorical cudgel to coerce neighbors. When Greek communists fled into Albania in 1949 following the civil war, Greek army officials considered invoking the doctrine, pressuring Albania to prohibit the use of its territory as a rear-guard base. Similarly, in 1986, Angola threatened to march into Congo if Congo continued to shelter and train the separatist Unita movement, forcing President Mobutu Sese Seko to investigate the evidence presented by Angola. And in 1984, the Soviet Union and Afghanistan warned Pakistan that they would pursue guerrillas into the country’s territory if necessary. Fearing an incursion, Islamabad scaled down its logistical support for the mujahideen.

Moreover, even a possibility of military action justified by hot pursuit can fuel wide-scale humanitarian crises. As one such example, Thailand relocated large refugee camps from its border areas into the disputed Kampuchea region in the 1980s to ward off possible raids by Vietnam in pursuit of Khmer Rouge. These relocations exacerbated the humanitarian emergency sparked by Vietnam’s 1978 invasion, which displaced a quarter-million Cambodians, worsening poverty and starvation.

Sometimes, the concept of hot pursuit is used to downplay incidental border incursions. Whenever South African forces entered Angolan territory, for example, they would claim to be in hot pursuit of Namibian separatists. (These excuses eventually gave way to a tacit admission that South African troops were there to support Savimbi.) Similarly, Daniel Ortega, Nicaragua’s president, repeatedly denied that his forces had invaded Honduras in 1986–87, as the two countries clashed over Honduras’ support of the anti-Ortega rebels. Yet he was willing to concede that Nicaraguan troops may have crossed the border in hot pursuit. The assumption in both cases was that raids undertaken in hot pursuit represented a less severe disruption of the international order than an outright invasion and carried an aura of legitimacy. 

Further complicating things, hot pursuit incursions often occur in the wake of civil wars, when fighters are in flight and borders are unsettled. Such incidents can complicate peace settlements, as violence merely shifts toward peripheral areas or spills across borders. This was the case when the United States chased Vietcong guerrillas into Cambodia during the Vietnam War and when Rwanda's Tutsi-led military pursued Hutu militants into Congo following the 1994 genocide.

Geopolitics often muddies the waters even further. Throughout history, the pursuing states tended to be small or medium-sized powers, but they often drew on the support of more powerful neighbors. For instance, when Hungarian forces briefly crossed into Austria in pursuit of Hungarian anticommunist rebels in 1956, they had the Soviet Union’s backing. In some other instances, the pursuing states were regional powers eager to rise through the ranks, such as the United States at the turn of the twentieth century when it chased Pancho Villa into Mexico. Smaller countries that neighbor such rising powers -- say, Vietnam (near China) or Georgia (near Russia) -- could act aggressively in response to their incursions, fueling regional instability.  

To be fair, the international community can invoke the right to hot pursuit for a just cause. In 1994, for example, a unanimous resolution by the UN Security Council permitted NATO warplanes to launch raids in Croatia using the doctrine as a justification. Croatia’s airfield had become a base from which Serbian rebels staged air attacks against the UN safe areas in nearby Bosnia. Although the strikes ultimately fell short of deterring Serbia, they demonstrated NATO’s resolve to stand up to its aggression. In another example, Malaysia called on a special UN police force to carry out hot pursuit strikes against drug smugglers in Burma’s lawless Golden Triangle.

In some other cases, countries mitigate the destabilizing effects of cross-border incursions by setting up buffer zones in which the use of external force would be acceptable. In the 1980s, Iraq and Turkey officially agreed to a few-mile joint security zone into which both could march. Mexico and the United States reportedly discussed the right of U.S. aircraft to pursue Mexican drug smugglers up to 100 miles into Mexico, but no farther. However, such efforts are more the exception than the norm, and hot pursuit often entails incursions deep into a neighbor’s territory. 


The tumultuous history of the term’s usage offers a number of implications -- political, legal, and normative -- for the U.S. fight against ISIS. The open-endedness of the phrase and the lack of a legal framework underpinning it would make for a rather unclear war mandate, potentially opening the door to chasing militants beyond Iraq and Syria. This could in turn set the precedent for border violations by other states elsewhere in the world. Altogether, there are several reasons why Washington should employ firmer international law in combatting extremism. 

First, the debate about invoking the right to hot pursuit too often falls prey to unrelated interests. An illustration is Turkey, a country whose role in the anti-ISIS campaign is pivotal. Turkey might well outrank the rest of the world in how often it has cited the hot pursuit doctrine in recent memory, using it to justify repeated ground incursions into Iraq to target Kurdish separatists. Yet when Washington requested more robust Turkish military support in combating the Islamists, Ankara refused to cooperate. Its two main fears -- of Kurdish separatism and of a resurgent Assad regime -- overrule its other security considerations. 

Second, the shock waves from past military interventions -- or from failures to intervene -- can significantly distort the calculus. During the height of the Iraq war, more than a few observers called for cross-border attacks into Syria to combat Islamic extremism. Back in 2007, for example, the national security expert Max Boot chastised the Bush administration for not authorizing special operations forces to hit terrorist safe houses in Syria, “even though international law recognizes the right of 'hot pursuit' and holds states liable for letting their territory be used to stage attacks on neighbors.” Striking Islamic militants at this early stage could have stemmed the growth of al Qaeda in Iraq (the precursor to ISIS that benefited from a steady cross-border flow of recruits) but was not pursued because Washington feared spreading the unpopular war beyond Iraq’s borders. Today, Washington might be hesitant to take similar strategically sensible action out of fear of becoming embroiled in another regional conflict. 

Third, the doctrine of hot pursuit has little legal validity on land, unless participating countries conclude a separate treaty spelling out such rights -- as the United States and Mexico did at the turn of the past century or Iraq and Turkey did during the 1980s. Validity cannot come from a country’s right to national self-defense. Although the two phrases have often been used interchangeably with regard to ISIS, they are starkly different. The UN Charter defines self-defense as actions necessary to preserve a country’s territorial integrity and political independence. This clause is meant to be invoked only under exceptional circumstances, such as when a nation is under direct attack. It is impossible to claim that Western strikes against ISIS are driven by the same imperative.

Yet with the emergence of new security threats, such as Islamic extremism, the two concepts are slowly growing interchangeable. Self-defense is increasingly used to describe security threats that are less consequential than a full-blown foreign attack, and hot pursuit is frequently invoked in deploying cross-border force, not meting out criminal justice. As a result of this conceptual slippage, the two terms risk bleeding into a one-size-fits-all excuse to justify every kind of international intervention.

This lack of clarity is certain to backfire. If the United States can carry out cross-border incursions into Syria on such weak legal grounds, then there is little to stop Russia from invoking the phrase in Ukraine, or China from apprehending Uighur separatists across its border. Even the nominally noninterventionist Brazil has jumped on the bandwagon to invoke the right to hot pursuit as a justification for its recent cross-border actions against drug lords in Peru. More fundamentally, if ISIS indeed poses an existential threat to the United States and its allies, the fight to destroy it should have better legal grounding than an arcane law meant to nab bandits on the high seas. 

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  • LIONEL BEEHNER is pursuing a Ph.D. in political science at Yale University. He is a member of USA Today's board of contributors and a former staff writer at the Council on Foreign Relations. 
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