As bad as the war in eastern Ukraine has already become, displacing more than a million people from their homes and costing thousands of civilians their lives, there is a possibility that it could be creating the conditions for an even worse conflict in the near future.

Eastern Ukraine is awash with weapons and armed militia groups on both sides. Right now, that situation is relatively controlled, because the groups are allied with their patrons in Moscow and Kiev, and they appear to be focused on fighting the broader war rather than trying to seize their own territory or exploit it for personal gain. But as the war goes on, or especially if it ends and those groups are left intact, that could change. If it does, then that could lead to a different kind of conflict — one that would be much more chaotic, more harmful, and more difficult to resolve.

As US policymakers consider whether to send weapons and other military aid to Ukraine, they should think carefully about whether that might escalate the conflict now — and lead to even greater chaos in the future.

How Ukraine could find itself mired in a new, even worse conflict

That process has already, to some extent, begun. The Kiev central government's authority has effectively collapsed in much of eastern Ukraine. It was too weak to fight the Russian-backed rebels and unacknowledged Russian forces on its own. So it turned to dozens of private "volunteer" militias that share the Kiev government's goal of crushing the separatists, but aren't necessarily operating under its full control.

At the moment, the groups on both sides are all at least loosely allied with a higher cause in the war: Russian-backed separatist militias are fighting for independence from Kiev, and pro-Kiev volunteer battalions are fighting to keep them from getting it.

But if the war escalates, those groups could grow more powerful, or spawn newer, more extreme factions. (Some are extreme already, such as the neo-Nazi Azov battalion, which fights on the pro-Kiev side.) As they grow stronger, they will have more and more incentive to use their increasing military strength to serve their own interests, especially if the broader cause that unites them falls away.

There are two main ways that eastern Ukraine's war could devolve into a second conflict. First, as the conflict drags on and militias become more powerful and perhaps more extreme, they could turn against one another, either over political disagreements or simply to compete for territory — something that has happened in other prolonged civil wars.

Second, if and when the war ends, Ukraine's government will want to retake control of the territory where militia groups currently operate. But those groups might not want to give up their territory, resources, and power without a fight. Such a fight might not be easy for Ukraine's weak government to win.

In either case, the result would be a self-reinforcing cycle of escalating violence — one that could eventually lead to warlordism, chaotic civil war, or both.

How this has happened before

This outcome is far from certain, and Ukraine might well manage to avoid it. But the possibility should not be dismissed. This is a story we've seen before, in country after country.

Look, for example, at Afghanistan in the 1990s. A decade of anti-Soviet insurgencies, supported by the US and Pakistan, had empowered mujahideen groups with arms, fighters, and territory. In the 1980s, the groups shared a common foe and fought for the common cause of Afghan independence. But when the Soviets withdrew in 1989 and their Afghan puppet regime collapsed in 1992, the country was left divided into fiefdoms controlled by individual warlords and insurgent groups. None wanted to give up their hard-earned territory, so they turned on one another.

That led to a civil war, the consequences of which are still with us today. As Columbia University political science professor Kimberly Marten noted in a 2007 paper, "popular disgust against warlordism in the mid-to-late 1990s helped the radical Islamist Taliban movement capture and hold territory." The US invaded to topple the Taliban government a few years later.

And in Libya, when Muammar Qaddafi's government fell in a civil war, it took the state security apparatus with it, opening up a power vacuum in the country. The post-Qaddafi government, to project its authority, turned to the same local militias who had helped win the war. A 2012 Foreign Affairs article warned that "the strategy of trying to dismantle the regional militias while simultaneously making use of them as hired guns might be sowing the seeds for the country's descent into warlordism." Indeed it did: today, Libya has shattered into a collection of warring factions, and there are signs — such as the recent emergence of fighters who claim to be allied with ISIS — that it might soon grow even worse.

Likewise, in Syria, as early as mid-2013, local leaders were warning that the fighting between rebels and Bashar al-Assad would create a second war, this one between moderate rebels and more extreme jihadist groups. That is, of course, exactly what happened.

These are extreme cases. Ukraine differs from them in some obvious ways. It is in many ways more stable than Libya or certainly 1980s Afghanistan, Ukraine's conflict is limited to the east rather than being nationwide, and it's entirely plausible that Kiev could retake control from the militias once the war ends. But the point is that there is a clear, well-established pattern in which militias and rebels become warlords, and warlords lead to long-term instability and more war. Eastern Ukraine is already plagued with militias. And that process is made more likely by corruption and institutional weakness — both of which Ukraine has been struggling with for years.

The private militias that might turn against the state, or one another

Marten wrote that countries' descent into warlordism often begins when "trained, armed men take advantage of the disintegration of central authority to seize control over relatively small slices of territory." In Afghanistan, for instance, that meant military leaders leaving the regular armed forces and setting up their own militias.

In eastern Ukraine there are already many groups of "trained, armed men" fighting on both sides of the conflict. On the separatist side, Russian troops fight alongside separatist militias, some of whose leaders are veterans of the Russian military. And on the pro-Kiev side, the government relies on privately recruited (and often privately funded) battalions of "volunteers" to bolster the official government troops.

There are early signs that these volunteer militias could threaten the country's stability in the future if they aren't brought under control now, even though they currently serve government interests. The Azov battalion's members espouse neo-Nazi ideologies and told The Guardian's Shaun Walker that they plan to "bring the fight to Kiev" after the war in the east ends.

In early February, when Ukrainian president Poroshenko was rumored to be considering disbanding the Aydar battalion, another volunteer militia, the group marched on Kiev. Its fighters blocked access to the ministry of defense and burned tires outside its gates until Poroshenko backed down.

Another militia, Right Sector, is a hardline anti-democratic nationalist group that has refused to even register with the central government. When one of their leaders was killed by Ukraine state security forces in March 2014, the group threatened revenge on Interior Minister Arsen Avakov.

Even if the war in eastern Ukraine ends favorably for Kiev, these militias would still need to be disbanded — and there is little reason to believe they would be willing to go quietly. And of course the separatist rebel forces currently do not serve government interests at all. Even if they fail in their secession attempt, there is no guarantee that they will disarm and become law-abiding citizens.

Both the separatist and pro-Kiev armed groups will have strong incentives to use their military power to pursue their own interests. If their interests conflict with those of the Ukrainian government, and the militias have the power to enforce their will but the weak government does not, that is a recipe for continued instability and conflict.

The militias are fighting for Kiev and Moscow today, but how long will that be in their interests?

To see the threat these groups pose, it helps to understand that the pro-Russia militias have ties to organized crime, which has long been a profitable enterprise and a path to political power in Ukraine. NYU professor Mark Galeotti, who studies organized crime with a focus on Russia, wrote in a May 2014 article in Foreign Policy that Ukraine has for years suffered from "endemic criminalization," and that the eastern Ukrainian city of Donetsk was home to "an infamous political-criminal circle" that formed "the heart of ousted President Viktor Yanukovych’s power base" and had ties to the Russian mob.

Pro-Kiev groups have organized crime ties as well. For instance, Galeotti noted, former Right Sector leader Oleksandr Muzychko, who was killed in a gun battle with government security forces, was wanted on charges relating to membership in an organized crime group.

There is no reason to believe that the militias, made even more powerful by the war, would not return to organized crime, making it both more necessary and more dangerous for the state to take them on.

And the oligarchs who sponsor many of these militias — and who would surely stand to lose if Ukraine's government ever moved against corruption — could use them to protect or even expand their influence. Even if they don't, those private armies could, simply by existing, be "creating enough of an implicit threat that the government can't move against, say, corrupt schemes," by the oligarchs that back them, Atlantic Council senior fellow Adrian Karatnycky warned me in an interview last week.

Keep in mind that these militias, even if they began as little more than thugs, are now powerful enough that they are fighting against national armies in a full-blown war. These groups have plenty of incentive to use their newfound military power to protect their interests from one another, or from the governments in Kiev or Moscow. Even if that means war.

If the US arms Ukraine, it could make this danger worse

The Obama administration is considering sending military aid to Ukraine to aid its fight against separatist and Russian forces. That could bring short-term military success. But it could also empower the militia groups, making a second conflict even more likely.

This would bear milder but disturbing parallels to US strategy in 1980s Afghanistan, when the US funded anti-Soviet militias that then turned against one another in the civil war that paved the way for the Taliban.

For exactly this reason, a group of influential experts has argued that Kiev should be required to disband the militias before the US sends weapons. That's a good idea, but it would also take some time to implement.

As the US becomes more concerned about Russian aggression in Ukraine, pressure and temptation to arm Ukraine now will grow, even if that means arming militias who could do far more harm than good. That strategy risks trading long-term stability for short-term military gains.