Why did the U. S. and the U. S.S. R use proxies to fight wars? Why not just fight each other?

the birthmark on georgiana's face alludes to the doctrine of "original sin," being tainted with evil from birth

although world war i began in 1914, the united states did not join the war until 1917. the additional firepower, resources, and soldiers of the u.s. to tip the balance of the war in favor of the allies. remaining neutral. when war broke out in 1914, the united states had a policy of neutrality.