So the whole Middle East is kind of a buffer zone between the west and Russia. That goes waaaay back in history, but most relevant to what’s going on today is the Cold War. That’s when pretty much the entire world was split up between Team America and Team Russia, which set the stage for proxy wars all over the world.
The western counties in the Middle East (Egypt, Kuwait, Saudi Arabia) have historically been puppeted by the US or Britain, with the exception of Syria. Syria belongs to Russia. And it’s important to Russia. Because it’s Russia’s only naval access to the Mediterranean. Without Syria, Russia loses the ability to fight a naval war with the West. So it’s really the keystone of that whole area.
Assad is sympathetic to Russia, which is why they have an interest in keeping him in power (no matter what he does), and why we have an interest in deposing him.
So on the surface, this is now another proxy war between the US and Russia. One which, out of all of our proxy wars, has by far the greatest potential to turn into a real war.