The eastern Ukraine conflict is typically seen as a war between the Ukrainian military, on one side, and Russian-backed rebels, fighting alongside unacknowledged Russian forces, on the other. But there is another faction fighting as well, one that has gone largely overlooked: the dozens of private "volunteer" militias that share Ukraine's goal of crushing the separatists, but that aren't necessarily operating under its control. These groups have proved useful to the Ukrainian government's war effort, but they pose a serious threat to the long-term stability of Ukraine.

By many estimates, there are approximately 30 of these private armies fighting on the Ukrainian side. Their fighters are accused of serious human rights violations, including kidnappings, torture, and extrajudicial executions.

The longer these groups continue to operate, the greater the chances that their leaders will exploit their power for personal or political gain, and cement their own power to operate without constraint from the central government. That undermines the power of Ukraine's government, risks chaos in a part of the country that has already suffered too much, and raises the possibility that even if separatist forces are defeated, eastern Ukraine might be left as an ungoverned collection of warlord-dominated fiefdoms.

Volunteer militias are fighting on the front lines — and growing in power

There are estimated to be about 30 volunteer, pro-Ukraine militia groups operating in eastern Ukraine. And while they collectively field thousands of fighters, their exact numbers are uncertain. Some, like the right-wing Azov Battalion, grew out of pre-existing groups that militarized when the conflict broke out in eastern Ukraine in 2014. Others, such as the oligarch-funded Dnipro Battalion, were created more recently.

The militias are allies of Ukraine's central government, and most coordinate with it, but they are not under its full control. The Azov Battalion, for instance, answers to the Ministry of the Interior, and receives considerable government support. By contrast, the unaffiliated Right Sector operates independently, and has refused to even register with the government.

As the conflict has gone on, these groups have proliferated and grown more powerful, making them useful in Ukraine's war effort, but also more of a long-term threat to the country and its government. Although most of the groups nominally report to either the Ministry of the Interior or the Ministry of Defense, that can break down on the battlefield. Steven Pifer of the Brookings Institution told me he found that military commanders on the front line cannot rely on the militias to follow orders. That is a worrying sign that the government does not have full control over the volunteer militias now, and that they could grow more independent in the future.

How Ukraine's political chaos created the militia networks

The roots of the militia groups date back to before the conflict. They are the product of a long tradition of mixing violent thuggery and politics in eastern Ukraine — one that laid the foundations of the current conflict.

There's been a tradition in eastern Ukraine of political parties allying with armed paramilitaries in eastern Ukraine for some time, according to Adrian Karatnycky, a Senior Fellow at the Atlantic Council. The city of Kharkiv, for instance, had been a "tough place for politics, where politics and violence crossed," for many years before the current crisis began, he said. Both pro-Russian and pro-European politicians relied on violent thugs to act as their political enforcers.

On the pro-Russian side, groups called Oplot supported former president Victor Yanukovych, who was known as close with Moscow, and would attack opposition supporters at rallies and demonstrations. To counter that, Karatnycky said, pro-European politicians "made common cause" with far-right Ukrainian groups who were willing to act as their political muscle. Their longstanding relationship, he said, "is of basically using them to secure physical protection for their demonstrations."

Those alliances deepened during the Euromaidan demonstrations, when, for instance, far-right activists provided support and protection to the anti-Yanukovych protesters in Kiev. When the conflict broke out in eastern Ukraine, armed groups on both sides were well placed to take a more significant role in the conflict and in politics.

The eastern Ukraine conflict made these groups of thugs more powerful

The nature of the eastern Ukraine conflict has given those thugs a battlefield — and turned them into better-organized, better-armed, and better-funded militias that are far more dangerous to Ukraine's future.

On the pro-Russian side, Oplot leader Aleksandr Zakharchenko turned his group into a full-fledged separatist battalion, leveraging his role as its leader into becoming "prime minister" of the self-proclaimed Donetsk People's Republic.

The conflict empowered the pro-Ukraine militias as well, because the Ukrainian military was too weak to fight the separatist insurgency on its own. When Russia annexed Crimea in early 2014, Ukraine had only about 6,000 combat-ready troops. The paramilitary "volunteers" bolstered the fighting forces, funded in part by private donations from wealthy oligarchs. Bands of politically motivated thugs grew into more substantial militarized battalions. There are now an estimated 30 "volunteer" militias fighting the separatists in eastern Ukraine.

The militias have also gained more power because the Ukrainian government, led by new President Petro Poroshenko, brought them friends in high places. For instance, Arsen Avakov, Poroshenko's Minister of Internal Affairs, was previously the leader of former Prime Minister Yulia Timoshenko's political bloc in eastern Ukraine. He has a longstanding alliance with members of the Azov Battalion, a far-right organization whose members have a history of promoting anti-Semitism and neo-Nazi views. Avakov has has used his position to support the group, going so far as to appoint Vadim Troyan, an Azov deputy leader, as the chief of police for the whole Kiev region. And Azov's leader, Andriy Biletsky, is now a member of parliament as well.

Igor Kolomoisky, an oligarch who is now the governor of the Dnipropetrovsk region of eastern Ukraine, funded the Dnipro Battalion, a private army that, according to the Wall Street Journal, has 2,000 battle-ready fighters and another 20,000 in reserve. Newsweek reported that he also publicly backs the Aidar battalion and has funded other militia groups as well, including the Azov, Donbas, Dnepr-1 and Dnepr-2 battalions.

The militias pose a serious threat to Ukraine's future

At some point, the Ukrainian government needs to be able to govern Ukraine. It can't do that if parts of the country are dominated by militias that don't obey any official authority.

The fact that powerful oligarchs are supporting some of the militias — and that Ukraine's oligarchs have a long history of resisting the state — raises the worrying possibility that these wealthy Ukrainians could use the militias to protect their interests from state interference.

Simply by existing, those private armies could be "creating enough of an implicit threat that the government can't move against, say, corrupt schemes," Karatnycky warned.

These groups pose a serious threat to Ukrainian civilians as well. In December 2014, pro-Kiev militias blocked humanitarian aid from reaching rebel-held areas of eastern Ukraine. Amnesty International researcher Denis Krivosheev said in a statement that the militias were starving civilians as a weapon of warfare, calling the tactic a war crime.

Another militia, the Aydar Battalion, has kidnapped and tortured civilians in eastern Ukraine. On dozens of occasions, militia members abducted civilians, tortured and interrogated them, and stole their money and valuables before either releasing them or handing them over to the Security Service, Amnesty International reported in 2014. The battalion was also reportedly running a secret detention center in the city of Severodonetsk, in which "detainees were forced to recite the Ukrainian national anthem and beaten if they failed."

Local police told Amnesty International that they had registered more than 38 criminal cases against Aydar members, but that they lacked the power to take any further action against the group — a worrying sign of the militias' power.

As time goes on, the things that made the militias useful for Ukraine will also make them dangerous. Their strength and autonomy in eastern Ukraine, particularly compared to the relatively weak government, could potentially give them tremendous power there. These are the conditions for warlordism — for militias turning their pieces of territory into little fiefdoms that they or their wealthy patrons would be free to govern, or exploit, as they wished.

Inevitably, Ukraine's government will have to take on the militias — which could spark a new conflict

The experts I spoke to agreed that the militias represent a threat to the long-term stability of Ukraine, and ought to be dissolved and incorporated into the regular security forces. But it's not clear whether Poroshenko's government sees that as a priority — or whether the government is equipped to take them on at all.

Karatnycky, of the Atlantic Council, said the militias had served an important purpose but that it was time for Ukraine to move to a purely professional military. Pifer agreed, saying that the militias are a threat to Ukrainian democracy, and that any increase in US military assistance to Ukraine — which he supports — should be tied to a commitment to dissolve the volunteer battalions.

However, it is not clear whether Poroshenko views that as a priority. Pifer said that he is certain that Poroshenko would agree, if pressed, that professionalizing the fighting forces is a good idea — but that it's not clear where that falls on the Ukrainian president's list of priorities. Poroshenko may be too focused on winning the conflict now, or on implementing other types of reforms, to take this potentially difficult step for long-term stability.

And it's not clear that he has the political capital to do so anyway. Avakov, his interior minister, backs the Azov Battalion, so would be unlikely to support any policy that would undermine it. And Avakov is a key supporter of Prime Minister Arseniy Yatsenyuk, who would likely need to be on board with any major change in policy on the militias.

It is likewise unclear whether oligarchs like Kolomoisky would be willing to give up their ties to militias and the power that they bring — and how they might respond if the Ukrainian government moved to disperse the groups.

The militias themselves might not go quietly either. In early February, when Poroshenko was rumored to be considering disbanding the Aydar battalion, the group marched on Kiev. Its fighters blocked access to the ministry of defense and burned tires outside its gates until Poroshenko backed down. In September 2014, The Guardian's Shaun Walker embedded with the Azov Battalion in Mariupol, and found "almost all to be intent on 'bringing the fight to Kiev' when the war in the east is over."

If they get their wish, it could be yet another disaster for a country that recently seems to have had little else.