This articles are perhaps too simplistic for those well versed in the situation, but I found them useful as an introduction to the ways various governments are intervening in Syria.

A video recently posted to the Internet depicting an improvised explosive device (IED) attack in Syria has garnered a great deal of attention. A Syrian militant group called the Hawks Brigade of the Levant claimed the attack, which targeted a Syrian government armored troop bus as it traveled along a road near a rebel stronghold in the Idlib governorate. According to the group, the attack depicted in the video employed a type of IED called an explosively formed penetrator (EFP). Though the video was shot from a fairly long distance away, it does appear that the IED punched a substantial and focused hole through the armored bus -- precisely the type of effect that would be expected if an EFP were employed against such a target.

Studying the IED technology employed by a militant group is an important way to determine the group's logistics situation and trajectory. It can also be a way to discern if a group is receiving outside training and logistical assistance.

Read More: Are Syria's Rebels Getting Foreign Support?

The ongoing unrest, violence and security crackdowns in Syria have been the subject of major international attention since February. Our current assessment is that the government and opposition forces have reached a stalemate in which the government cannot quell the unrest and the opposition cannot bring down the regime without outside intervention.

In the Dec. 8 Security Weekly, we discussed the covert intelligence war being waged by the United States, Israel and other U.S. allies against Iran. Their efforts are directed not only against Tehran's nuclear program but also against Iran's ability to establish an arc of influence that stretches through Iraq, Syria and Lebanon. To that end, the United States and its allies are trying to limit Iran's influence in Iraq and to constrain Hezbollah in Lebanon. But apparently they are also exploring ways to overthrow Syrian President Bashar al Assad, a longtime ally of Iran whose position is in danger due to the current unrest in the country. In fact, a U.S. State Department official recently characterized the al Assad regime as a "dead man walking."

We therefore would like to examine more closely the potential external efforts required to topple the Syrian regime. In doing so, we will examine the types of tools that are available to external forces seeking to overthrow governments and where those tools fit within the force continuum, an array of activities ranging from clandestine, deniable activities to all-out invasion. We will also discuss some of the indicators that can be used by outside observers seeking to understand any efforts taken against the Syrian regime.

Read More: The Syria Crisis: Assessing Foreign Intervention