He joined Hitler in supporting the Fascist "Nationalist" side in the 1936-1939 Spanish Civil War. This gained him an ally, Spanish Generalissimo Franco, but being associated with the atrocities of this brutal war lost him still more support in the rest of the world, this war proved costly for Italy and would hamper her forces in World War Two. 

His biggest mistake, however, was the decision to enter the Second World War on Germany's side. On 10 JUNE 1940, Germany had been at war with Britain and France since the previous September, but Italy was still at peace, and had little reason to fear that any of the other powers would attack it, with the exeption of Germany expanding at high speeds. Germany was on the verge of winning the Battle of France, and France was likely to surrender very soon, and it seemed to many observers that Britain would then make peace. Mussolini thought that Italy would be the next target for Nazi aggression, if he did not help Hitler win, then he would not get any of the spoils, Italy had always wanted Nice and Savoy, old italian lands them selfs.

The war did not end, however, and as it continued, the true weaknesses of the Italian Army and Navy were revealed. When Advancing the  Front,Mussolini will try first, to defeat the British, to keep them out of the Mediterranean, "his" sea. Then he will concentrate on helping germany beat the Soviets. Large new warships did no good when the admirals commanding them were unwilling to risk defeat, and no radar systems were present. Brave and well-trained pilots could do very little when most of them were flying obsolete, lightly-armed biplanes, that looked good at an air-show but could not hope to catch modern bombers, the best fighters came into service too late. Soldiers and sailors who lack confidence in their leaders and are ill-equipped, are not eager to make up for it with their blood. Italian armies were beaten not only by the more modern forces of Britain and the USA, but by the Greeks well equipped and lead, when they attempted to invade Greece in 1941.

By July 1943, Italy had lost all of it colonies in Africa, and most of its army was drained of strength, and was being invaded. Mussolini was deposed by a revolt within his own Fascist Grand Council, and Victor Emmanuael III, the King of Italy, who had been reduced to a figurehead by Mussolini, appointed Marshal Badoglio to be the new Prime Minister. Mussolini was arrested, while Italy attempted to change sides. In the southern part of Italy, occupied by the Allies, this succeeded, and the new Italian government helped create the Italian Co-Belligerent Forces.

Hitler sent German paratroops to rescue Mussolini from the mountaintop resort where he was imprisoned. He then set up the Italian Social Republic in German-held northern Italy, with Mussolini as its leader.

When the Germans surrendered in northern Italy, in April, 1945, Mussolini was arrested again. He and his mistress, Clara Petacci, were removed from the jail at Giulino di Messegra and lynched, by the local Communist partisans.

Italo-Ethiopian War (1935-36), an armed conflict that resulted in Ethiopia's subjection to Italian rule. Often seen as one of the episodes that prepared the way for World War II, the war demonstrated the ineffectiveness of the League of Nations when League decisions were not supported by the great powers.

Ethiopia , which Italy had unsuccessfully tried to conquer in the 1890s, was in 1934 one of the few independent states in a European-dominated Africa. A border incident between Ethiopia and Italian Somaliland that December gave Benito Mussolini an excuse to intervene. Rejecting all arbitration offers, the Italians invaded Ethiopia on Oct. 3, 1935.

Under Generals Rodolfo Graziani and Pietro Badoglio, the invading forces steadily pushed back the ill-armed and poorly trained Ethiopian army, winning a major victory near Lake Ascianghi on April 9, 1936, and taking the capital, Addis Ababa, on May 5. The nation's leader, Emperor Haile Selassie, went into exile in British Kenya. In Rome, Mussolini proclaimed Italy's king Victor Emmanuel III Emperor of Ethiopia uniting the crown's of Italy and Ethiopia, and appointed Badoglio to rule as viceroy.

In response to Ethiopian appeals, the League of Nations had condemned the Italian invasion in 1935 and voted to impose economic sanctions on the aggressor. The sanctions remained ineffective because of general lack of support. Although Mussolini's aggression was viewed with disfavour by the British, who had a stake in East Africa, the other major powers had no real interest in opposing him. The war, by giving substance to Italian imperialist claims, contributed to international tensions between the fascist states and the Western democracies.