Shiite Muslim volunteers from the Hezbollah Brigades march as they join the fight against jihadist militants of the Islamic State, on July 9, 2014, in Baghdad (AHMAD AL-RUBAYE/AFP/Getty Images)

Among the many complexities raised by the ongoing bloodshed in Iraq and Syria are the winding, shifting battle lines of the conflict, which has pitted a host of governments and ethnic and sectarian factions against each other. The jihadists of the Islamic State control a vast swath of territory in both countries and have set about targeting ethnic minorities, massacring uncooperative Sunni tribesmen and beheading Western hostages.

The regime of Syrian President Bashar al-Assad continues its indiscriminate bombing campaigns. Next door in Turkey, the government in Ankara fumes that a U.S.-led coalition is using its air power and military might only to hit back at the Islamic State -- and not also to address the problem of Assad. All the while, a patchwork of militias are making their own facts on the ground.

As WorldViews discussed briefly earlier, among the groups arrayed against the terrorists of the Islamic State are those also considered "terrorists" by the U.S. State Department and other governments. They are a reflection of the tricky politics of Washington's latest Middle East entanglement.

PKK

The Kurdistan Worker's Party, known as the PKK, is a Kurdish separatist organization that has waged a decades-long insurgency in Turkey. The Turkish government says the PKK, a Marxist-Leninist style guerrilla outfit that embraced a range of terror tactics at the peak of its armed struggle, has the blood of tens of thousands on its hands. The United States concurs.

But a peace process initiated in 2013 was meant to put the unrest to bed — yet that threatens to be derailed by the current crisis. PKK and PKK-affiliated units have been on the front lines in the fight against the Islamic State in both Iraq and Syria. PKK fighters helped the pesh merga of the regional government of Iraqi Kurdistan stem the advance of the Islamic State farther north into Iraq and were instrumental in the rescue of thousands of Yazidis, an ethnically Kurdish minority sect persecuted by the Islamic State.

In the Syrian border town of Kobane, fighters loyal to the PYD, a Syrian Kurdish organization affiliated with the PKK, have for weeks resisted an Islamic State siege beneath the glare of the international media, perched in nearby Turkey. The Turkish government was not impressed when air-dropped American munitions fell into the hands of the Islamic State; it was furious when reports emerged that U.S. officials had met with the PYD, which Turkish President Recep Tayyip Erdogan said was "equal with the PKK."

Hezbollah

The influential Lebanese Shiite organization has stood side by side with the Assad regime, which for years helped funnel Iranian weaponry and support to Hezbollah in Lebanon. It is listed as a terrorist group by the State Department for a range of activities. Hezbollah fighters have battled across the border with a host of rebel factions, including resolutely anti-Shiite Salafist militias such as the Islamic State and Jabhat al-Nusra (more below).

The Syrian war has spilled over into Lebanon in various forms, ranging from assassinations and car-bombings in Beirut to border clashes with rival outfits. Late last month, Hezbollah's chief, Hasan Nasrallah, warned Islamic State fighters infiltrating into Lebanon that they would be surrounded and face two options: "retreat or die of cold."

Hezbollah Brigades

In September, U.S. airstrikes helped a motley crew of anti-Islamic State militias to retake the Iraqi town of Amerli from the jihadists. These included fighters from the Katib Hezbollah (Hezbollah Brigades), a Shiite militia believed to be a direct proxy of Iran's Revolutionary Guards. The United States designated the outfit a foreign terrorist organization in 2009.

Veterans of Iraq's hideous sectarian warfare in the bad days after the U.S. invasion of 2003, the Hezbollah Brigades are full of their own zeal. According to one report, wary Kurdish soldiers who had to deal with them labeled the organization "Shiite Islamic State." In Amerli, Hezbollah Brigades fighters reportedly burned down the homes of Sunnis who had fled the fighting. "There is no way back for them," one commander told Reuters. "We will raze their homes to the ground."

Al-Qaeda

Al-Qaeda has a complicated relationship with the Islamic State. The latter was originally an offshoot of the former, but its gains this year have been so striking and its influence on global affairs so profound that even al-Qaeda felt compelled to repudiate this Islamic State upstart.

Al-Qaeda now has to vie for jihadist hearts and minds with the Islamic State; its launching of a new South Asian chapter could be seen as part of a concerted propaganda war with the jihadists now ensconced in Iraq and Syria. Al-Qaeda-linked militias such as Ahrar al-Sham and Jabhat al-Nusra have both fought with the Islamic State on occasion.

Jabhat al-Nusra

Originally the Salafist bogeyman many outsiders feared when sizing up Syria's Islamist rebel factions, the Nusra Front (or Jabhat al-Nusra) has been somewhat overshadowed by the Islamic State. Amid reports of a growing rift, the two organizations definitively broke ranks in February. That was accompanied by a statement from al-Qaeda that gave its full endorsement to Nusra and disavowed the Islamic State. Along with an alliance of other Islamist militias, Nusra has clashed intermittently with the Islamic State for months.

The al-Qaeda connection, as well as Nusra's hand in a spate of suicide bombings in Damascus, got it designated a terrorist group by the State Department, much to the chagrin of Syrian rebels who knew they needed the Nusra Front's help to combat Assad's forces.

Now, as U.S. airstrikes hit Nusra positions, it appears the militants are getting closer once more to the Islamic State. This week, they overran the main bastion in Idlib province of a Syrian rebel faction that the United States was seeking to strengthen. It's just another miserable wrinkle in a twisted, brutal war.