Foreign special unit mercenary soldiers (likely of Eric Prince ilk) were first imported into Syria to fire up and confuse an angry citizenry (much like in Ukraine). It was from this influence that violence from peaceful demonstrations began. More and more paid mercenaries came into the country.
Israel, which discovered oil in the Golan Heights (owned by Syria but controlled by Israel), wanted Syrian regime change so it could keep the Golan Heights where it also was getting 60% of its water supplies. Saudi Arabia and Gulf Emirate states wanted to run a pipeline through Syria to feed Europe.
The US, in league with Israel and Saudi Arabia, geopolitically wanted to create a Sunni state to separate Syria from Iraq and Iran. An alliance of Lebanon, Syria, Iraq and Iran would create a territory about the size of the United States within the region and this alliance would never cooperate with US economic interests.
So Saudi-influenced and financed Al Qaeda teamed up with disparate left-over elements of Saddam's Iraqi military forces and combined with imported soldiers brought into Syria. All three elements then combined with Syrians disenchanted with the Assad government.
A fake Free Syrian Army was formed and it received training, military equipment, intelligence and air support from the US. This new army became financed by the Saudis and other aligned nations. Originally, both Qatar and Turkey were part of this conspiracy.
The overthrow of Gadaffi in Libya enabled much of Libya's military weaponry, including chemical weapons, to become ratlined through Turkey into Syria, with Benghazi used as the staging area (see Seymour Hersh investigative reporting).
Also helping to transport this new army came enormous fleets of Toyotas and Mitsubishis which were converted into military-styled vehicles. Also came the well-knitted black-hooded uniforms for the new soldiers to wear.
https://syrianfreepress.wordpress.com/2015/10/12/toyota-mystery-solved/
All that was needed now was an excuse for the US military to gain a toe-hold in Syria. So next came the very well media publicized beheadings coupled with the announcement that ISIS now existed and it would establish a new Caliphate in the region.
With this now well-established the so-called Free Syrian Army became a minimized group as most of its members, now using US-provided military weaponry, joined ISIS to launch the Caliphate. Rapidly, this new military captured much of Syria and eventually captured Iraq's second largest city Mosul.
The original hope of the US, Israel and Saudi Arabia was the Bashar al-Assad presidency would be overthrown by the disparate military units and chaos would then reign. But Russia came to the rescue and everything changed. Politically unable to align with ISIS the US then built up a Kurdish military force, the SDF, and has used it as its proxy army in order to gain Syrian territory (50% of Syrias oil fields) to try and create a new state.
So this is where we are today. The ISIS fighters are paid. The Al Qaeda fighters are paid. The SDF Kurdish soldiers are paid. Fighters from each of these military forces are becoming well-groomed to participate in the international fighting forces of Eric Prince where they'll eventually get paid top-dollar!
What's sad here in America is that both Democrats and Republicans support this!