Why did the Soviet Union desire "defensible" borders and "friendly" regimes in Eastern Europe?

Thew soviets desired "defensible" borders and "friendly" regimes in order to compete and protect against the capitalist west.

Explanation:

The more red countries, the better. The farther away the enemy bombs are, the better. The more miles it takes to get to Moscow, the better. The more influence over the world, the better. The more allies with manpower and industry, the better.