The decision to invade Sicily was made by Britain and America at the Casablanca conference in January 1943, before Tunisia had been cleared of Axis forces. The combined British and American landings took place on 10 July on the southeast corner of the island, but German defence slowed the initial success down.
After the capture of Sicily there was great debate about the next step. By 18 June a decision was made to invade Italy. On 25 July Mussolini lost a vote of confidence and on 26 July the King of Italy, Vittorio Emmanuelle III, dismissed the fascist party from government. Armistice approaches were made to the Allies who hoped an Italian surrender could be coordinated with the planned invasion.
The invasion took place in two phases. On 3 September 1943 the British 8th Army crossed the Straits of Messina to the toe of Italy. On the 9 September, just hours after the formal announcement of the surrender of Italy, the Anglo-American 5th Army landed hundreds of miles up the coast at Salerno. The 8th Army under Montgomery wasted crucial time building up supplies instead of heading to meet the 5th Army at Salerno. As a result, the 5th Army beachhead was exposed to vicious German counter attacks and was almost defeated. The Allies moved across Italy and headed north where, about 50-70 miles south of Rome, they came up against a prepared defensive position the Germans had built across Italy - the Gustav Line. The line was the scene of bitter fighting for the rest of 1943 and the first half of 1944.
On 22 January 1944, in order to break the stalemate in front of the Gustav Line, the Allies decided on an amphibious descent on the western coast at Anzio. Allied forces were too slow to move inland and were soon desperately trying to hold off heavy German counter attacks that lasted until the end of February. At the same time, the offensive launched on 17 January to break the Gustav Line in the south was a costly failure. Attacks continued to fail until May, with Anzio remaining isolated in the north.
On 11 May the Allies launched another offensive against the Gustav Line. By the 18 May the Germans were breaking and a general withdrawal to the north took place with the British 8th and American 5th armies following. On 4 June Rome fell to the 5th Army. The Germans carried out a skilled fighting retreat over three months to northern Italy, establishing a new fortified line - the Gothic Line - covering the southern approaches to the Po Valley, the last barrier before the alpine passes into Germany.