And what we may be witnessing now are the opening shots of its next phase - the battle for control of the territory and population liberated by the fall of Raqqa and the death of the ISIS "caliphate".
"There isn't an over-arching United States strategy driving this", said Charles Lister of the Middle East Institute.
US -led coalition aircraft will be "tracked by the Russian ground and air anti-aircraft defense systems as air targets in the areas where Russian aviation is on combat missions in the Syrian sky", it added.
Sunday's downing of a regime jet prompted the Russian ministry of defense to announce that it would suspend the de-confliction hotline with the coalition, which is created to prevent any accidents in the skies over Syria.
Washington also described those strikes as self-defence.
Australia has suspended its airstrikes against Islamic State targets in Syria as a precaution after a US fighter jet shot down a Syrian warplane earlier this week.
The decision will not have a major effect on the air campaign in Syria, where Australia's F/A-18s rarely fly.
The action was a "flagrant aggression" that confirmed the US' "real stance in support of terrorism", Syria's military said.
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As the USA has intensified its fight against IS in Syria, Assad and his trusted allies of Russian Federation and Iran are increasingly asserting themselves. He spoke on condition of anonymity in line with regulations. In just over a month, USA forces have struck Iranian-backed Shiite militias in southern Syria three times, and on Sunday a U.S. F/A-18 shot down a Syrian Arab Air Force Su-22 jet. The 48-hour truce that had started there at noon Saturday was supposed to be extended.
Syrian government troops, for example, have reached the Iraqi border in an area where IS leaders and fighters have been gathering.
According to the United States, its aircraft fired on the Assad plane in defense of American-backed troops seeking to capture Raqqa, the Islamic State's (ISIS/ISIL) de facto capital in Syria.
While the United States military's shootdown of a Syrian jet on Sunday was a rarity in modern warfare, the first in 18 years, it was not an isolated incident.
Daraa-based activist Ahmad al-Masalmeh says fighting is now underway in the city.
A spokesman for the Revolutionary Guard, Gen. Ramazan Sharif, said all six ballistic missiles hit their targets, citing "local sources" and drone footage.
Davis noted Monday that most of the coalition's air operations occur east of the Euphrates, where ISIS has a larger presence, and that the USA has not seen behavior from Russian Federation that would "cause us concern".
More than 320,000 people have been killed since Syria's conflict began with anti-government demonstrations in March 2011.
Sharif told The Associated Press that the missile launch reflected Iran's "military power", though Iran has no intention of starting another war.