Iranian intervention in the Syrian civil war

From the 2000s until the fall of the Assad regime, the Islamic Republic of Iran and the Syrian Arab Republic were close strategic allies, and Iran provided significant support for the Syrian Ba'athist government in the Syrian civil war, including logistical, technical and financial support, as well as training and combat troops. Iran saw the survival of the Assad regime as being crucial to its regional interests.

Source: Wikipedia — Iranian intervention in the Syrian civil war (CC BY-SA 4.0)