✔ 最佳答案
Isis a terrorist group was formed in Iraq where the American army was. They knew that isis was forming and they didn't do anything to stop them.
Because Bashar Al Assad is a rational secularist who believes that Syria should be a modern country of tolerance and religious freedom, controlled by the Syrian people.
Isis grew and spread to Syria.
Western governments do not want a stable Syria (or Middle East in general). They seek to create a power vacuum and chaos that will give them a pretext to invade and install a puppet government. The West has supplied arms and money to the FSA and radical Islamist groups for this purpose.
They have an issue with Bashar Al Assad, they want him out.