Simple does it, huh?
Assads allegiance was to Saddam Hussein. Saddam Hussein’s main enemy was Iran.
Now, Assad had a control officer, owned by the outside. That control was a Saddam adviser, I forget his name. It’s here, somewhere. But he sold his services to whoever paid best.
For many years, he was actually run by the CIA,, so that Assad was a US asset. But alas, someone came along and paid better. And Assad changed “owner”.
His heart, though, is still with Saddam. Rock solid bet.
The ME is a complicated place