If you looked into this you would find out that Assad is in fact a mild-mannered English educated ophthalmologist who did not want to be President of Syria. He could have simply opted out and stayed in the UK and led an easy life. But he felt the honorable thing to do was to lead his country in this very tragic time. 

After you have done your research on Assad you can then investigate the sarin gas attack of 2013. At that time the UK/US and EU press were certain that the Syrian government had perpetrated a poison gas attack when it proved to have been Turkish in origin supplied by them to the Al Nusra head-choppers. 
https://www.lrb.co.uk/v36/n08/seymour-m-hersh/the-red-line-and-the-rat-line