In 1943, General Mark Clark became commanding general of the 5th Army in Italy and in 1944 he assumed command of the 15th Army Group, consisting of all Allied forces in Italy. He led the military operation called Avalanche. In this operation, the assault corps consisted of two corps: the US VI Corps, commanded by Maj-Gen. Ernest Dawley, and the British 10th Corps, commanded by Lt. Col. Gen. Richard McCreery. D-day was set for 9 September and the immediate objectives of the assault forces were to take Salerno and the airfield at Monte Corvino, to take the port city of Salerno and the port city of Naples and the surrounding airfields. Operation Avalanche was conceived by the Anglo-Americans amid much discontent and perplexity. The least convinced were the Americans who would have preferred to devote themselves to preparing the landing in Northern France, the real second European front. Although with a few exceptions, the British were pushing in a very different direction, privileging a peripheral, Mediterranean war of attrition, without frontal attacks on the strongest links in the Axis defence chain.

The compromise between these two contrasting visions was reached in May in Washington D.C. (Trident Conference), when a hypothetical date for the cross-Channel attack was finally given: 1 May 1944. On the same occasion, it was decided that once Sicily had been conquered, Eisenhower was authorised to take all necessary measures to push the Kingdom of Italy out of the war and force the Germans to commit as many forces as possible to the defence of the Axis soft underbelly.

For these reasons, the planning of Avalanche was overshadowed by cutbacks and uncertainties, and decidedly inappropriate resources, beginning with the leadership chosen for the operation.

The shortcomings of the men and means Clark had at his disposal also added up to some errors in approach. The Gulf of Salerno was in fact considered by the Germans to be an almost taken-for-granted target, because it represented the point of maximum extension of air protection that Allied fighters could guarantee from the available airfields. Yet Clark gave up the fleet's pre-emptive cannonade of the coast in the futile hope of catching the enemy by surprise. Furthermore, it divided the forces by placing the 6th US Army Corps south of the Sele river (the 36th Infantry Division, with the 45th in reserve on ships) and the British X Army Corps (the 46th and 56th Divisions) north of the same river.

Furthermore, in 1945, General Clark was head of the US occupation forces in Austria and US High Commissioner for Austria. As deputy to the US Secretary of State, he negotiated a treaty for Austria with the Council of Foreign Ministers. As commander-in-chief of the UN Command, General Clark signed a military armistice between the UN Command, the North Korean army and the Chinese People's Volunteers in Korea in 1953. In 1953, General Clark accepted the presidency of The Citadel, where he served for twelve years. After retirement, he was appointed President Emeritus of the college. General Clark died in 1984 and he is buried on The Citadel campus next to Mark Clark Hall.