system
Given the following post, respond as if you're commenting on Reddit:
human
Official Thread: ISIS

This is the official thread for the current situation in the Middle East. 

We've been getting dozens of questions for the past month or so, so let's pool all of our explanations, questions, etc. in a central location! 

Thanks guys :)
gpt
ISIS is an extremist group of Sunni Muslims whose stated goal is to establish a new caliphate in the Middle East.  A caliphate is an Islamic Empire, and its leader (the caliph) is said to be a successor to the prophet Mohammed.  ISIS follows a very strict, conservative interpretation of Islam, labeling all who don't comply as infidels, and promoting their deaths through jihad.

The group goes all the way back to the late 90s, when it was a smaller and less organized group.  It went through a few different names and made different countries its targets.  However, during the US invasion/occupation of Iraq, it gained a lot of traction in disputed regions, and a lot of fighters joined to fight the Americans.  It renamed itself the Islamic State of Iraq (ISI), and it became well-organized.  It also gained the financial support of Al-Qaeda.

After the US troop surge in Iraq, ISI had to retreat to some of the more remote areas of Iraq, and its numbers dwindled.  However, since the US has pulled out of Iraq, lesser security and sectarian tensions have allowed it to re-flourish.

More recently, Syria began a civil war against their president, Bashar Al-Assad, in 2011.  Because Syria shares a border with Iraq, it was easy for ISI units to move into the disputed areas.  ISI had been able to recruit a great number of rebels in Syria to join its organization, as they were already willing to fight against their current government.  Renaming themselves ISIS (Islamic State of Iraq and Syria), they have made incredible gains against Al-Assad's government.  However, holding so much territory (and the military assets/infrastructure within) has very nearly turned ISIS into a de-facto nation, and it has also given them the strength to better project force into Iraq.

At this time, ISIS controls about 2/3 of the area of Syria and 1/3 of the area of Iraq.  They are infamous not only for their warring and extremism, but also for their cruel treatment of prisoners and captured locals.  They have been raping and murdering everywhere they go, as well as human trafficking.  They also have more or less made terrorist threats against pretty much everyone and everything non-Muslim (including historical Buddhist shrines).  They have become so extreme, that even Al-Qaeda has recently denounced them.