This war started with Bashar Al-Assad succeeding his father in 2000. He promised his people change from his father's ways. He became president and nothing changed.
"In March 2011 Syria’s government, faced an unprecedented challenge to its authority when pro-democracy protests erupted throughout the country. Protesters demanded an end to the authoritarian practices of the Assad regime."
The Syrian government used violence to stop the protests. Assad decided to have his military take action in these protests by shooting at them. He made extensive use of police, military, and paramilitary forces. By 2012 the conflict had expanded into a full-fledged civil war. The protesters become what is known as the rebels.
In January 2012 Al-Qaeda breaks from the Rebels and forms their own group. Around that time also the Syrian Kurdish groups break from Assad's rule and fight against the government and alongside the rebels.
Iran, which is Syria's greatest ally, intervenes on Assad's behalf. Because of all the fighting that is happening between the groups, he puts his soldiers on the ground and supplies resources for Syria. Around that time also is when the rich oil Gulf States give supplies to Turkey. Turkey then supplies the rebels with both the Gulf State's supplies and also their own.
In August 2012 Assad uses chemical weapons against the civilians.
Originally, before the chemical attacks on Syria, other bystanding countries did not want to fight. But after an attack with chemical weapons on August 21, the US and Europe considered a military intervention.
On September 14, Russia and the US reached an agreement to postpone a US attack if Assad gives up his chemical weapons stockpiles by mid-2014.
After finally backing down from wanting to bomb Assad, the US trains the rebels and finally becomes a participant in the war.
After training the Rebels for a while, something happens to transform the war completely and effects not only Syria and surrounding countries but the US too. A group separates from the Rebels and joins the war out of different beliefs. They called themselves ISIS. ISIS doesn't fight Assad and the government, it fights the other rebel groups.
Russia then intervenes and says it will bomb ISIS, but only bombs the rebel groups.
In the past 5 years the UN has estimated that at least 250,000 people have been killed.
According to the United Nations High Commissioner for Refugees, 4.8 million have fled to Turkey, Lebanon, Jordan, Egypt and Iraq, and 6.6 million are internally displaced within Syria. Meanwhile about one million have requested asylum to Europe.