when your neighbors open up their borders to allow terrorists to cross into Syria, then no nation on this earth can seal its borders ( maybe their own side but not their neighbor's side)... You have Turkey where terrorists are sheltered, trained and then sent to Syria, every terrorists that is coming from Europe, Chechen, and etc enter Turkey first (Many reports and documentaries document that is it is very credible, even anti-Syria media reported it).. now from the south you have Jordan, where terrorists from gcc go to enter Syria, and then you have Lebanon Tripoli where it hold F$A terrorists, and there is Iraq who also is fighting terrorism... thus you have Turkey and Jordan who opened up their borders to terrorists to enter, and in addition you have Israel who allowed terrorists to enter, and they treat terrorists and send them back to fight.... all of that can't be controlled....
and the rest of your questions regarding religion or Shia vs Sunni, it all strated when the west invaded Afghanistan and Iraq...
regarding oil and gas, last year four field of gas and oil were discovered that can produce the same amount as of Kuwait only four fields, and there is more fields, I opened up a thread regarding that... now those field will kill the gcc role in Europe when it comes to oil , Syria is closer to them...
The SAA side is better of now then it was in 2011, 2012, 2013, the opposition controlled a lot more territory back in those years 2011 mainly, they were united as a FSA group, now it's all Islamic, Jihadi and divided, no FSA flag to be seen. Homs fighters drop their weaponry and leave.
What does that indicate ^^ ?
Yet people don't want to look at the realities