If we talk about the US attempts to destabilize Syria it's been there since 9 decades, could be earlier with the establishment of the Zionist movement in the USA and only increasing ever since. They were thinking by weakening the country slowly they'll be able to take it out easily without sweat, then realized it's more difficult than all the ones they took over combined. Hard evidence and blatant involvement to take over the country using the anti-Islamic Muslim Brotherhood proxies were set from the early days of the current 'Arab Spring' and the previous fail attempt 1976 - 1982.