In Iraq the Kurdish forces of the autonomous Kurdish north have proved to be the most effective Iraqi troops available. But the Kurds are not bulletproof. Recently the Kurdish government revealed that from mid-2013 through May 2016 the Kurdish forces lost 1,466 men (and a few armed women) killed while fighting ISIL. That comes to about 600 per 100,000 a year (a standard measure of such things). That compares favorably to the experience of foreign troops (mainly American) in Iraq between 2003 and 2011. From 2004-7, the deaths among foreign troops ran at 500-600 per 100,000 per year. After al Qaeda was crushed in 2007, the U.S. death rate in Iraq dropped to less than 200 dead per 100,000 troops per year and to nothing by the time American combat troops left at the end of 2011. Contrast that with the death rate for U.S. troops during Vietnam, Korea and World War II, which was over 1,500. Better body armor, tactics, training, weapons and medical care have all contributed to this sharp reduction in fatal combat losses.
The Kurds got the same results by eagerly adopting American weapons, equipment and tactics. Most Kurdish fighter have been trained by American and British advisors since the early 1990s and absorb the Western combat methods better than any other Moslem nation in the Middle East. The Kurds were also able to arm and equip their most heavily engaged combat units to U.S. standards and that played a role in keeping losses down, as did the availability of American air support and continued training assistance. Kurdish military and political leaders encouraged the use of the Western policy of keeping wartime losses as low as possible. This was a necessity for the Kurds who, like the Israelis, are surrounded by much larger, and often heavily armed, hostile populations.
In contrast the death rate of Iraqi security forces since mid-2014 have been about 2,000 per 100,000 per year. It was worst (about 3,000 per 100,000) in 2014 but was less than half that in 2015 and is lower still in 2016. It is unclear exactly how many troops, police and pro-government militia are actually available as the usual (for thousands of years) practice in this region is for commanders to inflate the number of armed men they command and pocket the money they receive for the missing “phantom” troops. One reason so many Iraqi officers and government officials wanted all American troops out of the country as soon as possible was because those foreign troops would often go and count the number of troops actually present and then report the real number. That number was almost always less (often a lot less) than the official number. When U.S. forces left in 2011 the Iraqi security forces (mostly army and paramilitary police) had about 300,000 armed personnel organized in over fifty brigades. While the Kurds comprise only about 17 percent of the Iraq population by early 2015, after the ISIL offensive had done most of its damage to Iraqi security forces there were only about 400,000 armed personnel Iraq could depend on and over a third of those were troops belonging to the autonomous Kurds in the north.
While the Kurds are the most effective Iraqi fighters, they also have their problems. Kurdish popular sentiment strongly favors an independent Kurdistan and the current Kurdish leadership openly promises a vote on independence “in a few years.” But the Kurds also have internal problems which the pressures of war have made worse. The biggest problem is that the Kurds in northern Iraq have long been split by clan rivalries. This has been a major reason why the Kurds were never able to create their own country. Despite numerous failed efforts to unite, the Kurds continue to squabble. This is happening again as the two main Kurdish political parties in the north, the KDP (Kurdistan Democratic Party) and PUK (Patriotic Union of Kurdistan) are moving in different directions. The two parties agreed to unify in 2006 and that has largely worked. But with more foreign aid coming in the PUK accuses the KDP (which holds most top leadership positions) of taking more than their share. To make this worse Iran is offering direct aid to PUK and, according to the KDP and many in the PUK, trying to divide the Iraqi Kurds.
There are other divisions, like the PKK (separatist Turkish Kurds) and similar groups in Syria and Iran. Turkey, Syria, Iraq and Iran have always sought to keep the Kurds divided and less capable of forming a Kurdish state out of the portions of Turkey, Syria, Iraq and Iran the Kurds have lived in for centuries. Despite that since the early 1990s Iraqi Kurdistan has effectively been autonomous and far more stable and prosperous than the rest of Iraq. Attempting to establish a separate Kurdish state would bring problems not only with Iraq (which probably couldn't do much about the matter anyway), but also with Turkey and Iran, both of which have restive Kurdish minorities. Normally Syria would protest as well, but currently Syria is torn apart by civil war. Speaking of which, a decade ago the two Kurdish parties were openly discussing declaring independence in response to a Sunni-Shia civil war in Iraq. That war never happened, largely because the Sunni minority was not strong enough and still aren’t.
At that time (2006) the Kurds probably had some of the most capable military forces of any of the factions in Iraq, and that included the government. The PUK had some 40,000 militiamen, and the KDP nearly 60,000. In addition, between them the two groups have about 50,000 reservists as well. Most of the militiamen were (and still are) armed and trained as motorized light infantry, and organized into 36 brigades of several thousand (or more) active duty personnel. There were some "armored" units equipped with Russian tanks, APCs, and artillery. There is also a small, but effective artillery force. In addition to these forces, there were an estimated 15,000-20,000 Kurds in the Iraqi Army or National Police, and a further 10,000 or so working for private security organizations. Since 2006 the unified Kurdish military has remained at about 100,000 with a larger but with a larger and better equipped reserve. In effect there are about 300,000 armed and trained (some minimally) Kurds in the north. Most are part-timers only activated a few months a year.
But because of fear that the Kurds will become too powerful militarily the Shia Arab controlled Iraqi government has quietly and unofficially blocked delivery many arms bought for use by the Kurds. The U.S. has always urged upgrading the military equipment of the Kurdish forces but has also supported the Iraqi government. That means it is up to that government to distribute weapons it buys and since Mosul fell in mid-2014 the Kurds have been getting louder about their weapons shortages. While the U.S. still refuses to ship weapons directly to the Kurds some other NATO countries have done so. But most of the weapons the Kurds need are still being held by the Iraqi government.