Before the war, Assad wasn't a democratic and "liberal" leader like we western people imagine to be perfect, but he was secular. But he also had to fight islamist ideologies, so he reacted rather harsh to critics, but I never found any evidence that could put him on the same level as his father.

Then the "Arab Spring" started, and states like Egypt and Libya were tageted by revolutions. And, especially in Libya, the rebels where supported by the wahabi Monarchies (Saudi Arabia, Qatar). Soon after that, there were people in rallying in Syria, at the start there were mostly peaceful protests, and I imagine Assad to be a little bit jumpy at that time, seeing what happened to Qaddafi. So when there were reported clashes between police and protesters, the west say the police started, Assad and "buddies" say the others started, the violence escalated.

At that time some sunni military deserters started to work against Assad. Also a lot of people from outside the country streamed into the country. At that time, western media still called these people brave "patriots/heroes" (these people were joining ISIS and al-Nusra). In relatively short time there has formed the FSA, partly supported by the USA. At that time Assad already warned the west that the "noble rebels" are nothing but jihadists and many of them aren't even syrian. And the west called this propaganda and ignored it.

A little bit later as the violence already escalated, chemical weapons were used and execution vidoes were made. The west accused Assad, that he used the chemical weapons, he said the rebels used them, while no military party was hit, only civilians, Assad allowed the west to investigate the case and to destroy remaining chemical weapons. (The strike happened close to pro-Assad military positions by the way.) The main narrative the west used in the following months was that the rebels never would have been able to use those weapons, disregarding that not just former syrian military was on the rebels side, but also former iraqi military from ISIS (still a part of al-Nusra at time). The chemical weapons is dug up from time to time to "prove" how evil Assad is, but I personally haven't seen any convincing prove yet.

After that Isreal started airstrikes against the syrian army, who, even before the rebellion called for military actions against Assad, because he sponsored Hezbollah. At the same time ISIS grew stronger (still financed from outside) and separated from al-Nusra, and used an effective video propaganda method to call even more people to fight Assad and also Shia in Iraq.

Through all this time Assad told the west about the Jihadists, plundering, beheading and installing Sharia law in conquered areas, but the west not just ignored it, but also supported them at least indirectly.

Some bonus information: Syria and Libya decided to stop using the Dollar to trade. I'm not saying this is any proof, but it makes you think if there are any ulterior motives, since there are much more oppressing rulers in the Middle East than Assad, which are western allies.