Question

How did the Soviet invasion of Afghanistan contribute to the fall of the Soviet Union?

Answer 1

The answer is '4'.
The Soviet economy crumbled further due to the heavy military cost of the invasion.  
The U.S. provided financial support to push them out and shorten the conflict.  The Red Army did suffer a loss of face but the collapse of the Soviet Union happened because military expenses drained their economy to such an extent that normal, everyday expenses could not be met.  

Answer 2

Answer:

Four

Explanation:

The soviet economy was damaged and it crumbled, because the military could barely keep up with invasions.