This is the first of a two-part series on proxy war. This first essay explains why states might engage in proxy war and the likely costs and problems. The second will examine the same issues from the proxy’s perspective.

A proxy war occurs when a major power instigates or plays a major role in supporting and directing a party to a conflict but does only a small portion of the actual fighting itself.

Proxy war stands in contrast not only to a traditional war—when a state shoulders the burden of its own defense (or offense)—but also an alliance, when major and minor powers work together with each making significant contributions according to their means. So the United States working with the Afghan government against what’s left of al-Qaeda and the Taliban is more of a traditional alliance because of the major U.S. role, with thousands of American troops and hundreds of airstrikes, while Iran working with Houthi rebels in Yemen is a proxy war because Iran primarily provides weapons and funding, not its own troops. How much direct military support is too much to count as a proxy war, of course, lies mostly in the eye of the beholder, but in general, think the lower end of the involvement-spectrum. Iran’s support for the Syrian regime, for example, involves relatively few Iranian forces but a lot of foreign Shiite fighters from Afghanistan, Pakistan, Iraq, and Lebanon as well as helping direct the Syrian regime—so more proxy than alliance.

Syria is no exception for Iran, which uses proxies in many of its conflicts: the Lebanese Hezbollah, an array of Shiite militias in Iraq, and the aforementioned Houthis in Yemen, among others. Russia uses proxies in Ukraine, and the United States often does so in its operations in the Middle East and Africa, supporting the Kurdish “People’s Protection Unit” against the Islamic State in Syria and working with armed groups in Libya to fight terrorists there. Indeed, much of the U.S. struggle against terrorism in parts of Africa and the Middle East involves working with local forces or governments to get them to more aggressively go after groups linked to al-Qaeda or the Islamic State. By design, it is the proxy, not the United States, that is doing much of the lifting, with the United States providing intelligence, using special-operations forces, and deploying drones to maintain a light footprint.

States use proxies for many reasons. For the United States, the issue is often cost: Locals fight, and die, so Americans do not have to. In addition, because they are local, proxies are often (though not always) more accepted by the affected communities. Therefore, they can better gain intelligence from those communities and are less likely to promote the sort of nationalistic backlash that so often accompany foreign interventions. If the proxy is a guerrilla force, they often know the terrain better and can blend in with the population in a way that foreigners never can. Most states lack the power-projection capacity of the United States and turn to proxies as a way to influence events far from their borders. Iran lacks a navy or massive airlift capacity necessary to sustain large forces in Yemen: Supporting the Houthis, however, gives Tehran influence there nonetheless.

For many states, however, factors other than cost and fighting power come into play. Some of Iran’s proxies, such as the Lebanese Hezbollah, are ideological soulmates, and advancing them helps advance Iran’s broader revolutionary agenda. States at times back proxies because they enhance a leadership’s credibility at home: An array of Arab governments often backed Yasser Arafat or other Palestinian leaders, many of whom they loathed, in order to burnish their Arab-nationalist credibility among domestic populations that saw the Palestinian cause as the beating heart of Arab identity.

Proxies also offer a way of fighting that can limit escalation. States often deny that they are supporting proxies—Russia, for example, claims not to be involved in Ukraine despite funding an array of groups opposed to the government of Kyiv, arming and supporting them with its own forces. At times, other states may not know about foreign support or at least the extent of support, but in others it is a convenient fiction: Not knowing, or at least not having to know because a rival trumpets its support publicly, allows a government not to respond when it would prefer to avoid the matter. The United States cooperates with Pakistan on counterterrorism and operations in Afghanistan, and Islamabad’s denials that it is providing massive support for the Taliban allow a façade of amity. All this makes escalation harder, or at least limited to a certain arena. Israel, for example, has warred repeatedly against the Lebanese Hezbollah but has not struck Iran directly despite Tehran’s massive financial and military support for the group. But if Iran, rather than Hezbollah, attacked Israel with a missile, then Israel would feel compelled to strike Iran itself. This is especially important for Iran, which cannot match Israel economically, militarily, or even diplomatically given the Islamic Republic’s global pariah status.

Yet for all these advantages, proxy warfare has many risks. Despite the power asymmetry, proxies almost invariably act according to their own interests and impulses. Right after 9/11, the United States asked the anti-Taliban Northern Alliance, its key Afghan ally made up primarily of minorities, not to take Kabul so that a force composed of ethnic Pashtun, Afghanistan’s dominant community, could do so and assuage the fears of minority dominance. The Northern Alliance did so anyway. In another case, the United States sought to kill Islamic State fighters as its local Kurdish and Arab proxies retook their territory, but the proxy was often pleased to let the fighters slip away from key strongholds like Raqqa and gain the territory without a bloody battle: They wanted the territory, not a high body count. This independence creates a tension for a proxy’s patron. A stronger group is a more effective proxy, but a more effective proxy has a greater ability to stay independent.

Such independence often risks dragging the sponsor into an unwanted conflict on behalf of its proxy. Palestinian guerrilla cross-border raids sparked conflicts with Israel, leading to a back and forth that created political pressure on the guerrillas’ erstwhile Arab-state supporters who hosted them and at least pretended to support their efforts. Wars in 1956, 1967, and 1982 grew out of these dynamics, with Syria and Egypt being sucked into the fray. Indeed, by giving a group money and support, it may become more reckless, knowing, or at least hoping, that a major power is behind it and would bail them out in the face of trouble.

Proxies are also often corrupt, brutal, and incompetent. Just as sponsoring states are often happy to fight to the last member of the proxy group, so too are many proxies happy to cash their sponsors’ checks and do little in return. The United States spent millions training various Syrian opposition-group members, but in the end only a handful showed up for the fight. Proxies’ brutality may not matter to some power: Russia and Iran, gross human-rights violators themselves, presumably care little about the abuses of their proxies. The United States, however, is often tarred with the behavior of its proxy, making it difficult to sustain domestic support.

Support for a proxy often leads other states to back their own favored horse, worsening the overall conflict. Lebanon, for many years, saw Iran, Iraq, Saudi Arabia, Israel, Syria, and other powers regularly meddle and support rival factions, often solely because one of their great power rivals was doing so. This, in turn, increased the independence of the proxies as they could threaten to turn to other powers if they felt unsupported.

Once the spigot of cash and weapons to a proxy opens up, it is hard to close, particularly for a democracy like the United States. To gain or solidify domestic support for aid, the sponsoring power often talks up the proxy’s cause and the heroic nature of the fighters, making it harder to walk away from them. Programs and even entire bureaucracies develop, creating vested interests in continuing the fight. Iran’s Islamic Revolutionary Guard Corps, for example, is tasked with supporting pro-Iranian revolutionary forces; as its role outside the country expanded, so too did its influence inside. Weak groups and states are often masters of the political dynamics in their patron’s country, manipulating the media and domestic support there to get the sponsor to do their bidding.

A state can impose intrusive monitoring and reporting requirements, but these are often expensive, and in any event they usually rely on the proxy for information and reduce plausible deniability. At times proxies can be pushed, educated, or wheedled into better behavior, but too often the United States can only move the dial a little. States can try instead to choose the “right” proxies, but they are usually few and far between. At times, as in Afghanistan, Iraq, and Syria, the United States is usually choosing among varying degrees of bad.

If the United States is going to engage in proxy warfare—and it is going to—then Americans need to recognize these limits and problems. At the same time, the United States should not overestimate Iran, Russia, or other adversaries. Those states too will face willful, abusive, and incompetent proxies, and their abilities to achieve their foreign policy goals are likely to suffer as a result.