The Allied invasion of Sicily began on 10 July 1943. The US Seventh Army commanded by General Patton, and the British Eighth Army under Montgomery, landed respectively at the Gulf of Gela and south of Syracuse. While Montgomery's forces encountered stubborn resistance in the hills around Mount Etna, Patton's troops advanced northwest towards Palermo and directly north to sever the northern coastal road. They then moved eastwards supported by a series of amphibious landings along the north coast, reaching Messina ahead of the British. By the end of August, Sicily was under Allied control and could be used as a base to invade Italy.
On 3 September 1943, the Eighth Army landed at Reggio (on the 'toe') and began its slow slog up the boot of Italy. Five days later, the US Fifth Army landed at Salerno, encountering heavy German resistance. At this point the Italian government agreed to an armistice with the Allies (publicly announced on 8 September). Mussolini was dismissed by King Victor Emmanuel III and placed under arrest by his successor, Badoglio, but was rescued by Hitler's airborne commandos. Mussolini became head of the Salo Republic in German-occupied Gargagno in northern Italy. Badoglio, who had escaped to Pescara, established a government under Allied protection. On 13 October, the Italian government declared war on Germany.
British Commonwealth forces now advanced up the east coast, capturing the port of Bari and the airfields around Foggia. The US, meanwhile, inched up the western side of the boot, encountering increasingly difficult terrain and strong defences. A series of mountains, ridges and rivers prone to sudden flooding presented a formidable natural barrier which complicated Allied commanders' plans.
German forces withdrew to the Gustav Line south of Rome, which included the heavily-defended hilltop monastery of Monte Cassino. In January 1944, the Allies launched an amphibious assault on the western port of Anzio. Operation Shingle, launched on 22 January, took the Germans by surprise. Allied troops, however, failed in their attempt to thrust inland and cut off German troops on the Gustav Line, instead becoming bottled up in the beach-head they had established.
Between January and May, four major offensives were launched to break the Gustav Line. The objective was finally achieved by a combined assault of the Fifth and Eighth Armies (including British, US, French, Polish, and Canadian troops) along a twenty mile front between Monte Cassino and the western coast. Monte Cassino was captured on 18 May. As the German defences disintegrated, forces at Anzio broke out of their beachhead and moved up the coat towards Rome. Following the liberation of the capital on 4 June, Badoglio resigned and a new anti-fascist government was formed under Bonomi.
German troops now retreated to the Gothic Line. Their resistance condemned the Allies to another harsh year of campaigning. Many Allied units had been withdrawn to be used in Operation Dragoon (the invasion of the South of France launched in August 1944), and progress was slow. It was not until April 1945 that the Allies launched an overwhelming offensive that broke through German positions, and forced the surrender of German Army Group C on 29 April. Four days earlier, Mussolini had been caught by Italian partisans as he tried to escape north to Switzerland. Along with his mistress, he was shot and his corpse put on public display in Milan. Hostilities formally came to an end in Italy on 2 May 1945.