As the Islamic State has continued its shocking military advances throughout Syria and Iraq recently, much has been written about its seemingly unstoppable battle capabilities. But there's one force that has scored a number of successes against its forces: the Syrian Kurdish militia known as the People's Protection Units, or YPG.

Though originally linked to the Democratic Union Party (PYD), the most powerful Kurdish political party in Syria, the YPG is now seen as the armed force of all of Syrian Kurdistan. The PYD is also affiliated with the Kurdistan Worker's Party, or PKK, a group classified as terrorists by the US, the EU and Turkey, among others.

The YPG has previously not really been active in the battle against the Islamic State in Iraq because they were prevented from entering by the dominant Iraqi Kurdish party, the Kurdistan Democratic Party (KDP). Following the recent losses by its armed forces, the peshmerga, however, the YPG and other PKK forces have entered Iraq to fill the vacuum and fight the Islamic State (formerly known as ISIS). And they have proven to be pretty damn good at it.

Fierce battles are raging between the Islamic State and the Kurds on several fronts extending from the Syrian border town of Rabia to Sinjar and, further south, from Kirkuk to Jalawla. The Sunni militants have been defeating reputable Kurdish peshmergas in some important battles, forcing them to withdraw.

Kurdish officials say the rapid progression of the Islamic State is due to its fighters having up-to-date US weapons seized from the Iraqi army during recent advances in Mosul and other cities. This has forced the peshmergas to retreat, and Kurdish officials have become outspoken in requesting weapons from Western governments that would enable them to fight the Islamic State effectively.

The YPG, however, has been fighting the Islamic State and its predecessor for over two years in Syria. The group recently prevented the Islamic State from advancing in the strategically important area of Syria's Hasakah province, which neighbors Iraq's Nineveh province. Had it not been for the successful intervention of the YPG, the Islamic State would have merged the regions and posed a bigger threat both to Syria and Turkey, which borders both provinces.

After the Islamic State seized Mosul in June, it also made an effort to reach the oil-rich city of Kirkuk. Peshmerga forces moved in quickly, however, and prevented the insurgents from seizing the city. There were some reports then that the YPG was called in by Iraqi Kurds, yet these reports were not officially confirmed until recently.

On August 10, YPG spokesperson Polat Can announced from his official Twitter account that its special anti-terror units have been in Kirkuk and Jalawla fighting with peshmergas against the Islamic State for a month.

RAST?YEK YPG: Grupên me yên Taybet berî niha bi mehekê li gel pê?mergeyan li Kerkûk û Celewla ?er li dijî DA?? dest pê kirin. — Polat CAN ????? ??? (@polatcano)August 10, 2014

In northern Syria, another significant, and ongoing, battle between the YPG and the Islamic State is taking place in Kobane. In June, the Islamic State launched a large offensive against the predominantly Kurdish city which was supported by tanks and other armored vehicles, including US Humvees brought from Mosul. Despite these new weapons and heavy manpower, the Islamic State was not able to seize the region and suffered heavy casualties. As a result, its plans to merge the Kobane region with neighboring Raqqa, which serves as the Islamic State powerbase, failed.

After the Islamic State increased its attacks in Iraq, YPG forces also crossed into the country on August 2 to protect the Rabia border crossing. According to Can, this move was done on request of the Iraqi Kurds and in coordination with the peshmergas. After heavy fighting, the YPG seized control of the border and town of Rabia.

As of now, there are currently hundreds of YPG fighters in Rabia, Sinjar, and Kirkuk actively fighting against the Islamic State on several fronts in Iraq. There is video footage online of peshmerga thanking the PKK forces for coming to the rescue, and stating that without it they would have perished.

On another front, local media reported that PKK fighters had a critical role in the fighting in the strategic town of Makhmur, which is only a half hour away from Erbil, the heavily populated capital of the Kurdish region.

With these recent actions, calls have increased for the PKK to be removed from the terror list. An online petition was launched this week asking the White House to delist the group.

Iraqi Kurdish experts have attributed the success of the YPG and PKK forces to their advanced military skills and long years of guerrilla warfare experience. Despite a ceasefire that has been in place for over a year now, the PKK fought against Turkey for decades, and some commanders of the YPG either came from or were trained by the PKK.

The solid discipline of its fighters also seems to be another significant advantage for the YPG.

Perhaps the most important role the YPG has played during the recent crisis was rescuing thousands of Yazidi Kurdish civilians who were stranded on Sinjar mountain. After the Islamic State took control of the only road connecting Sinjar to the Kurdish regions, YPG fighters managed to break through IS lines and open up a safe passage for the Yazidis. Thanks to this, thousands of Yazidi children, women, and elderly were able to escape to Dohuk, Zakho, and other safe regions through Kurdish controlled areas of Syria, with the armed support of YPG.

According to Yazidi eye witnesses, the YPG and peshmergas are fighting alongside local Yezidi units led by renowned Yazidi community elder, Qasim Shesho.

This is Qasim Shesho, the Yezidi hero who didn't flee Sinjar & is fighting with his honourable tribe against ISIS. — Hamo (@KekHamo)August 8, 2014

Although some significant progress was made in Sinjar thanks to the Kurdish forces and US airdrops, UNHCR estimates between 20-30,000 are still trapped in the mountains facing death by starvation and dehydration. After reports on UK's Channel 4 News, calls are being made on the British government to send heavy-duty Chinook helicopters to speed up the evacuation process of the remaining desperate refugees.

It looks like in this chaotic atmosphere, one positive thing has developed for the Kurds — they have emerged relatively united against their enemy. At the time of writing, Massoud Barzani, the president of Iraqi Kurdistan, had just met with commanders from the PKK. Reports of the meeting stated a deal was reached between the previously fractious groups, and that they would be forming a union to combat the Islamic State.