The first and most important thing to understand about the ongoing civil war in Syria and Iraq is that it is not two wars in two nations. It is one war between two religious groups. From Tehran to Beirut there is an ongoing war between the Sunni and Shia Muslims -a war which dates back to the very founding of Islam. It is not a fight that will be solved by western military intervention.
The current conflict arose when peaceful demonstrations against the Assad regime in Syria were met with brutal suppression by government forces. As the bloodshed of the mostly Sunni protestors grew unbearable, Sunni troops, units, and leaders of the Syrian Army defected and formed the Free Syrian Army. Early success led them to capture a number of Army and Air Force bases which supplied them with weaponry to fight effectively against the government forces.
Who is ISIL?
ISIL stands for Islamic State in Iraq and the Levant. The actual acronym name of the group in Arabic is DA'SH. You will see it rendered inaccurately in western media as ISIS Islamic State of Iraq and Syria. The “SH” sound actually represents “Sham” -a reference to Greater Syria, which extends from southern Turkey to the Sinai. Their territorial ambitions are much larger than the inaccurate western name implies. The map below designates the areas covered by “Iraq and Sham”. This is the area that they envision as the nucleus for the re-establishment of the caliphate.
This group is a splinter of Al-Qaeida, originally being Al-Qaeida in Iraq. They fell under the influence of an Iraqi terrorist, Abu Bakr AlBaghdadi (real name Awwad Ibrahim al-Badri al-Samarri), who was a protege of Osama bin Laden. After the death of bin Laden, he has refused to recognize the authority of the new Al-Qaeida leadership and has taken his own initiative in Iraq and Syria. The ISIL fighters are from all over the Muslim world. Many of them have engaged in the jihadi wars in Afghanistan, Iraq, Libya, and Yemen. ISIL was initially welcomed by Syrian rebels in their fight against the Assad regime. Much of the original training was done in Afghanistan, Pakistan, and (ironically) Iran. They have fought in so many theatres with such a wide range of equipment that they are familiar with almost anything they find on the battlefield.
After ISIL entered Syria, there was an initial power struggle between Jabhat Al Nusra and ISIL. Jabhat Al Nusra was the original AlQaeida group in Syria. ISIL tried to exert authority over them and bring them into ISIL but the leadership refused and AlQaeida ruled that they should fight alongside one another in cooperation. ISIL refused this ruling and began taking control of areas of Syria and independently governing them. They have captured an oil producing region of Syria, and the revenues from black market sales fund their continuing operations.
ISIL government has imposed a very harsh Sharia law upon the populations. Women are warned to stay at home. Hands will be chopped off from thieves. Any unIslamic business is forbidden. Extreme punishments including execution by sword are visited on any who oppose the ISIL government. Now large segments of Syria and Iraq are under these harsh laws.
The ISIL are so savage, and the populations under their control have cried out so loudly, that the other rebel factions have turned on them to expel them from Syria. You have to be ruthlessly savage to be kicked out of AlQaeida for being too extreme. Currently ISIL and the Assad regime do not fight one another. Both of them fight the rebels, who are caught between the government and even more extreme Islamists.
What is the Shia-Sunni war?
The Sunni Shia war dates back to the power struggle between the fourth caliph (leader of “all” Muslims), Ali (cousin of Mohammad), and the followers of a powerful Syrian leader named Muawiyah. Ali was ultimately assassinated by one of his former followers who belonged to the Kharijites, a group who broke away because Ali was not strong enough in asserting his authority as Caliph. Muawiyah became the fifth Caliph and the followers of Ali (thereafter called the Shia) refused to recognize him. The war ended in a bloody battle (Karbala) where Ali's son was killed and the Caliphate passed firmly into the hands of those called Sunni. This battle is remembered each year in their highest holiday of mourning by the Shia, who have not forgotten the killing of their leaders even after 1400 years.
This is key -the current Sunni-Shia war is being fought in these regions of Syria and Iraq just as it was 1400 years ago. The Caliphate passed back and forth from Sunni to Shia hands over the centuries, but the struggle to control Islam has not lessened. In modern times, Shia live mostly in Iraq and Iran, with smaller groups scattered in places like southern Lebanon and Syria (The Alawites).
Who are the parties other than ISIL?
Iran (Shia) is the largest factor in the current war. When the (Sunni) rebellion in Syria began to threaten the Assad regime (Alawite Shia) Iran stepped in to support the Assad regime. In addition to sending their own militants (Shia) to fight in Syria, the Iranians also hired unemployed Iraqis (Shia) as fighters to defend the Syrian government. More importantly, Iran mobilized the Hezbollah (Shia) forces in Lebanon to move into Syria and fight on the side of the government.
As the rebels were overwhelmed by the Shia groups, surrounding Sunni countries sent fighters to help the rebels. AlQaeida in Iraq (Sunni) sent Islamist fighters to start the Jabhat AlNusra, with some funding from Qatar. Saudi and Kuwaiti (all Sunni) money funded the Free Syrian Army. The US (supporting both Sunni and Shia) has committed itself to fund and support the Free Syrian Army.
The Syrian Kurds have taken control of the northeastern region of Syria. They have avoided any clashes with government forces, claiming instead to be subject to the regime. Jabhat AlNusra had frequent clashes with the Kurds in the second year. Currently the Kurds are avoiding the conflict.
Update: The Kurds entered the conflict i the summer of 2014 after being attacked by ISIL and losing territory to them. With US air support the Kurds have made significant advances against ISIL.
Who is fighting whom? (Shia vs. Sunni)
In both Syria and Iraq the fight is a religious one. In Syria the (Shia Alawite) Assad regime has the weakened Syrian Army, and a powerful Air Force that is in the hands of Alawite officers and crews. They are joined by Iranian, Iraqi, and Lebanese Hezbollah fighters, all of whom are Shia.
The rebels are fragmented groups. The Free Syrian Army is Sunni, and relatively moderate, though there are strong Islamist tendencies. There is a collection of smaller Sunni militias allied with the FSA. Jabhat AlNusra is a group of Salafist Sunni fighters from around the Muslim world that was sent to Syria by AlQaeida. These groups form a liberation front together. When ISIL first entered Syria, they were allied with this group.
The FSA/rebel groups are now fighting ISIL, whom they consider too extreme. ISIL is not currently fighting the Assad regime. The Kurds are currently not fighting any group. The Assad regime and Shia allies are fighting the FSA/rebel groups.
What about Iraq?
The same ISIL group that sent Jabhat Nusra and ISIL into Syria are leading the fight against the Iraqi government. They number only a few thousand, but like the Pied Piper, they are collecting other anti-government groups on their march toward Baghdad. These groups are not loyal to ISIL, but will fight beside them against the government.
The Kurds have used this opportunity to move in to protect Kirkuk, which they consider their historic Capital. They will not leave Kirkuk without a fight, so the government may engage them at some point. The Kurdish Peshmerga may be the best soldiers in Iraq at this point.
The Shia Iraqi government has called home Shia troops from Syria. They are mobilizing Shia militias to protect Baghdad. Iran is sending troops to defend the Shia holy sites in Iraq.
Can ISIL take Baghdad?
That is possible, but not probable. We have not seen the Iraqi Army fight yet, so there is no sure answer. The Shia are very strong in that region. So far, ISIL has been in “friendly territory.” There is also the likelihood that the Iraqi Air Force would be supplemented by air strikes from the US carrier group moving into the region. A siege of Baghdad is likely at this point, with some Sunni neighborhoods going to the rebels and the government holding important areas. Beirut was divided by sectarian violence for over a decade (and really still is today), and fighting in Damascus, though not heavy, has followed the same pattern.
What does this mean for the US?
If the US intervenes in Iraq, it will mean the commitment of Air and Special (ground) forces to strengthen the Iraqi government. We will be allies of Iran in this fight. We will be aiding a government that is allied with Iran, Hezbollah, and the Assad regime. We will be on the Shia side of the fight.
In Syria, the US is already committed to supporting the other side of this same fight. We will be supporting the FSA against the government, Iranian, Lebanese, and Iraqi Shia foes. We will be on the Sunni side of the fight.
Imagine if you will, an Iraqi Shia militia that has enjoyed US support, training, and air support. They cross the border into Syria and now engage a Sunni FSA unit that has enjoyed US support, weapons, and training. We are now on both sides of the same fight.
This is a Sunni-Shia religious war. This war is over 1400 years old, and is being fought by the same sides and in the same region that it was 1400 years ago. The party of Caliph Ali (Shia) is opposing the caliphate of the Sunni on the same battlefields where they fought so long ago.
What about Lebanon?
For now Lebanon is safe. The government has taken precautionary steps of rounding up and arresting suspected ISIL sympathizers. We are fairly distant from the current events. The ISIL is the group who set off the series of car bombs in Lebanon earlier this year, so there is a possibility of renewed violence. If Baghdad should fall, which is unlikely, then the situation becomes much more grave.
Update: A small ISIL force moved into the Arsal region of Lebanon in the summer of 2014 in a surprise incursion but was repelled by the Lebanese Army. They are currently surrounded and living in caves in the border region, where they still hold perhaps 2 dozen soldiers and policeman captured in their surprise attack.
A final map of the intertwined and complex relationships involved: