Before Russia got involved in the Syrian conflict, Turkey had supported ethnic Turkish militant groups in Syria and fought Bashar al-Assad. (Video via Channel 4)
Not just that, Turkey alleges Russia was attacking the ethnic Turkish groups it was supporting. (Video via Al Jazeera)
The U.S. has famously supported other Kurdish fighters in Iraq who have taken on ISIS in the country, but more recently, Russia has allegedly supported them, too. (Video via Vice)
The New York Times reported last month, Turkey had called upon Russia's ambassador to the country and was concerned that Russia was helping the Kurds.
So, while Turkey says it warned the Russian jet repeatedly before shooting it down, it wouldn't have taken much to bring tensions to a boil.
This video includes images from Getty Images.