On Tuesday morning, the Turkish military said it shot down a Russian fighter jet on the Turkish-Syrian border.
Turkey, a NATO member, says the Russian jet violated Turkish airspace. Russia has denied this.
In a news conference, Russian President Vladimir Putin called the act a "stab in the back delivered to us by accomplices of terrorists" and added that "today's tragic event will have serious consequences for Russian-Turkish relations."
This latest development adds another complicated layer to the ongoing Syrian conflict, in which the key players have varying regional interests and priorities.
Citi Research's chief global political analyst, Tina Fordham, put together a brief cheat sheet listing the key players in the Syria conflict and some of their motivations.
Notably, this chart is missing some non-state actors, including members of the Syrian opposition who are fighting to remove President Bashar Assad. Many of those groups are given funding and weapons by the CIA, Saudi Arabia, and Turkey.
If you need a quick refresher, take a look below:
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