system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What's happening in Syria?

What's this war over? What does each side want? Why is it happening? I know there's threads about it but they're from two years ago, I'm looking for a more up to date explanation, I didn't follow it as I don't like politics and the depressing news that surrounds us, but you can't avoid hearing about it, I want to know now.
gpt
In 2011, during the Arab Spring, protests began against Syria's President, Bashar al-Assad. Assad was from a minority group called the Alawites--who are Shi'ite Muslim--while the majority of Syria's population was Sunni Muslim. The Assad government was known for being repressive and authoritarian, and as protests spread through the Middle East against similar authoritarian governments (and more importantly *winning* against many of those governments), the Syrian population protested to. However, Assad responded by calling in the military, who proceeded to try and crush the protests with force. However, this only intensified the protests, who began to arm themselves. Units began to defect from the military, and the protest began to take on overtures of an armed rebellion against the government. 

The conflict escalated until mid-2012, and government forces attempted to use more and more measures to regain control of the country. This included mass artillery and air strikes against the rebels, who were trying to organise a government and army to fight the Assad regime. However, the rebel groups were not unified. They were a collection of various forces, ranging from pro-democracy forces to elements of al-Qaeda and other extremist groups. This meant that the rebel groups had many different goals, and often times fought each other. While the rebels are numerous, the government's forces are often better equipped, leading to an effective stalemate between the two as they fight over cities and towns. 

The war also began to take on sectarian and proxy war tones as it seemed to shift away from 'government vs. rebels' to being a part of the larger Shi'ite v. Sunni divide in the Middle East. Assad began to receive aid from various Shi'ite powers, including Iran, while the rebels received aid from various Sunni powers, such as Saudi Arabia. In addition, while other states have tried to push for a concerted effort to aid the rebels, Russia and China have been using their veto powers in the UN Security Council to block such efforts. The fractious nature amongst the rebels have also hindered efforts by the West to intervene, as many rebel groups have ties to organisations that the Western powers would like to avoid supporting. Not to mention, the Iraq War has soured much of the US populace on the idea of military intervention. 

As a result of the fighting, a massive humanitarian crisis has developed as nearly a quarter of the entire Syrian population has fled the country. These refugees have fled to neighbouring nations, and many are trying to make it to Europe. This has led to the current humanitarian crisis in Europe. 

This doesn't even go into the roots of the Syrian rebellion, such as the role of colonial era divides imposed by the French and British, the rise of ISIS, the Kurds, and a wide variety of other topics. However, hopefully it's enough of an overview to give you a basic idea of what's going on. 

**tl;dr:**
What's this war over?: Originally government forces against pro-democracy rebels, now a proxy war between various powers supporting various groups in Syria
What does each side want? Syrian government forces want to restore their control of the country, Rebel forces vary widely. Some want a democratic Syria, others want an Islamist state. Kurds want their own independent country, etc. etc. 
Why is it happening? People protested. Government responded with force. Civil War broke out. Outside powers supported different groups on both sides of the War.