Ukraine asks Turkey to close Bosphorus and Dardanelles straits to Russian ships
The request puts NATO member Turkey in a difficult position
Russia invades Ukraine
Russia has launched a barrage of missile, artillery, and air attacks on Ukraine early Thursday
Why Has the U.S. Sanctioned Russia in the Past? (infographic)
The 2014 invasion of Ukraine and seizure of the Crimean Peninsula is the top reason why the U.S. has sanctioned Russian individuals