Several motivations are operating simultaneously. One is offered by Phil Greaves of Global Research: “There are predominantly two parties to blame for the sectarianism rife in Syria and spreading beyond its borders, they are: Saudi Arabia and Qatar. Sitting behind these states, and driving their destructive policy is, as always, the Empire of the era. Those who gain the most from destabilizing whole resource-rich regions for their own benefit. For the last 60 years, that Empire has been the United States of America.”
A second explanation is the hypothesis of Paul Craig Roberts: “Perhaps the purpose of the wars is to radicalize Muslims and, thereby, destabilize Russia and even China.”
A third reason is held by many, including both Greaves and Roberts, which is that destabilizing Syria allows Israel to achieve its aims.
Fourth, for both the U.S. and Israel, this is a means to undercut Hezbollah, which is sponsored by Iran.
Fifth, the neocon agenda long ago was to roll up the “axis of evil”, including Iran and its ally Syria. Their agenda is world domination by the sole surviving superpower.
Sixth, the military-industrial complex and its lobbies on the Hill thrive on the profits, the work of war, the advancements, and the demand for their services that instability brings. The DHS thrives on an atmopshere of war and fear. Members of Congress thrive on making speeches about promoting rights and democracy, even though they are promoting war, instability, refugees and death. The State Department appears to have abandoned diplomacy and become subservient to the neocon influences.
Seventh, the U.S. has a ready-made pro-war interest group in many churches.
Eighth, important leaders and politicians believe their own rhetoric about spreading democracy, being anti-dictators, building progressive states, and eliminating certain kinds of weapons. These beliefs accord with being anti-Second Amendment. They are parts of the ideology of “liberalism”, which arose as classical liberalism faded out and was replaced by its opposite of nationalism, expansionism and progressivism.
How can the U.S. and its NATO allies can get away with these policies? What are the long-term effects of these policies? Those are separate and important questions too.