Proxy wars became common during the cold war because they allowed the soviet union and the united states to:

a. resist each other's growing influence without directly going to war.
b. avoid engaging in a costly and protracted arms race.
c. protect their weaker allies from destructive military conflicts.
d. weaken the military-industrial complexes that had developed in each country

A. resist each other's growing influence without directly going to war.

Explanation:

The US and the Soviet Union never engaged directly in the war, rather than resorting to war between them they supported wars in other countries.

Each band supported aside and this strategy enabled them to keep growing in influence and promote their national security at home.

The major examples of proxy wars include the USSR Afghanistan War, the Yom Kippur War in Israel, the Vietnamese War and the war in Koreas.

While the USSR supported communist movements, the US aided the opposite side, and this dynamic came to an end in 1991 with the end of the Cold War.

The collapse of the USSR meant an end to this and created further issues in the ex republics belonging to the socialist side.