Syria's civil war began 7 years ago — look back at how it spawned ISIS, a refugee crisis, and a massive US strike

Thursday marks the seven-year-anniversary of the start of the Syrian Civil War.

The conflict has reportedly claimed the lives of as many as half a million people, caused the worst refugee crisis since WWII, and destroyed so many cities and so much infrastructure that the cost to rebuild is an estimated $200 billion. 

What started as street protests turned into a civil war, and has now erupted into a war that involves dozens of nations (directly or indirectly), hundreds of armed groups, and four main sides.

Despite all that, the war continues — and shows no real signs of stopping anytime soon.

Take a look here at how the conflict unfolded:

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In the spring of 2011, a series of pro-democracy protests known as the Arab Spring were rocking countries across the Middle East. In Syria, people peacefully protested in the streets after President Bashar Assad's government arrested and tortured teenagers for writing pro-revolution graffiti on their school wall.

Source: BBC

To quell the protests, government forces started opening fire during marches and sit-ins. With hundreds of people now killed by Assad's government, the protesters who initially called for more civil liberties started demanding a total overthrow of Assad's regime.

Source: The Guardian

With no end to the violence, some former government officers formed the Free Syrian Army to support the opposition. Other armed groups with various ideologies and loyalties would also be created. As sides battled for control over major cities such as Homs and Aleppo, the fighting escalated into a full-blown civil war by the end of 2011.

Source: BBC