1- despite them declaring non-belligerence in 1939 under the terms of the pact of steel they were required to come to the assistance of Germany in the event of war
2- Mussolini had a change of heart after a series of sweeping victories by Hitler in France, the Netherlands and Belgium and the British evacuation at Dunkirk, it appeared to Mussolini that the west were on the brink of total collapse
3-Mussolini had resented their neutral position and refused to even use the erm ‘neutrality', he was a bellicose nationalist who was not prepared to sit in Rome, while the map of Europe as redrawn, especially after he had scorned the neutrality of Liberal Italy in ww1, by 1940 he saw Italy becoming a second-class nation that was going to miss out on the territorial gains available, the scale of the German successes in 1940 made these territorial gains seem like a distinct possibility and even silenced doubters
4- the allied collapse left a neutral Italy in a German-dominated Europe in a vulnerable position, Mussolini feared that a Germany angry at Italy for failing to honour its treaty obligations could well use its power against Italy with the result that the country could lose its Germany speaking valleys in the north of the country
5- Mussolini was very keen to revive a close relationship with Germany to boost his prestige, as well as maintaining the great power status that Italy had in theory more than in practice
6- in March 1940 Germany had promised to make up the shortfall in coal that would result from a British blockade of Italy by sending 12 million tons annually by rail, as much of Italy's Mediterranean trade was disrupted by the war, it became increasingly dependant on Germany and when a British naval blockade prevented German coal exports from reaching Italy this only determined Mussolini to enter the war
7- he hoped war would distract from domestic problems