The correct answer is A) they strengthen the Allied counter-attacks.
American soldiers influenced the war in Europe in that strengthen the Allied counter-attacks.
When American troops arrive in Europe to participate in the war they helped to counter-attack the enemies attack in the Western European front to end the war with a victory. They helped to stop the German Army. They fortified the Allied forces and droved the German troops back to Germany. After the war, US President Woodrow Wilson established 14 points to establish permanent peace in Europe.