The two conflicts have cast the United States and Russia as enemies in one war and nominal allies in the other.
Syria’s territory has been fragmented after four years of war. The government now controls only a fraction of the country.
Kurdish ground forces have been America’s main partner in the war against ISIS in Syria. But the partnership poses delicate problems for the United States.
Kobani has been the focal point of the U.S.-Kurdish battle with ISIS. American airstrikes have hit more than 1,000 targets there, almost half of all their strikes in Syria, helping the Kurds push back ISIS in the north.