Question

After World War II in 1945, what would explain why Soviet leaders wanted a buffer of satellite countries between the Soviet Union and Germany?

Answer 1

Russia had no secure border. Following the devastation faced by Soviet Union in WWII, they wanted to push the border away from Kiev, from Moscow & Minsk 
The Yalta Agreement between FDR, Churchill & Stalin had laid out the spheres of influence that each of the Allied countries would have, and the satellite countries all fell under the Soviet sphere.