Expanded from an earlier answer of mine

The Italian Army did not emerge from the Second World War with a stellar reputation. Some of this opprobrium was unearned. Italian troops may have suffered from deficiencies in equipment and logistics, but they were capable of putting up a stiff fight. It also bears mentioning that some of the Italian military fiascoes were due to both interference from Mussolini as well as indifference to Italian needs by their German allies. The Italian contingent to Barbarossa was a political gesture to the Axis alliance rather than a seriously planned component of the invasion. Not surprisingly, Italian equipment broke down in terrain it was not designed for and its troops suffered from lack of heavy of equipment as the campaign dragged on. As the Barbarossa example indicates, there was a real disjuncture between the political aims of Mussolini and the armed forces' ability to execute them. This discrepancy between aims and goals as well as Fascism's civil-military relationship often combined to make disaster one of the hallmarks of Italy's military efforts in the first half of the war.

As foolish as it looked in retrospect, Mussolini's decision to join the war on the side of the German in June 1940 had a certain logic to it from Mussolini's perspective, and should be understood from those terms. Italy's fateful leap on 10 June represented the intersection of three overlapping factors that had long been at play within Italian foreign policy: opportunism, ideology, and Mussolini's ambition to make Italy into a great power.

Pietro Nenni, an exile from fascist Italy, trenchantly Mussolini's analyzed Mussolini's invasion of France as the epitome of opportunism in 1940:

without sense, without possible justification, and without honour. Without sense, because no real Italian interests whatever were at stake. Without possible justification, because a German victory would impose on Italy, as on the rest of Europe, the intolerable and brutal hegemony of Hitler. Without honour, finally, because Mussolini is attacking a France already occupied and in deadly agony, thereby assigning to Italy the role of a jackal.

Although Nenni was an opponent of the regime, there was a great deal of accuracy in this statement. Mussolini had spent the winter of 1939 playing off the Germans and the Allies, the latter often represented by American intermediaries, for Italian belligerency. Once Mussolini realized that Germany's strength appeared ascendent in Norway and the initial stages of Fall Gelb, he decided to cast his lot with Hitler. Mussolini was quoted as saying that all he needed was a few thousand dead to earn a proper place at the negotiation table and for Italy to get both French territory and booty. There was much to suggest that Mussolini thought the war at June 1940 was almost all but over and this would be a way for Italy to be on the winning side at the last minute. Ciano's diaries suggest that Mussolini was increasingly nervous about the war and he felt that for Italy to make no decision would have meant that Italy would receive nothing and lose its gains in the Mediterranean and Africa. This fear ensured that when Mussolini perceived that one of the warring powers was in ascendancy, he would intervene at the decisive moment for Italy to gain the maximum amount of territory postwar.

This conceptualization of Italy as a "weight in the scales" was actually an Italian policy that had a long pedigree in both Fascist Italy and its liberal predecessor. Mussolini was not the first Italian leader to be likened to a jackal; Bismarck was actually quite fond of characterizing the Italians as opportunistic diplomatic scavengers. This opportunism reflected the fact that Italy was arguably the least of the great European powers and sought to maximize its limited military and economic clout by intervening at key points. Mussolini was very much aware of these restrictions and aggressively sought to have Italy break out of these bounds. Here Fascist ideology helped as it held that war and action could transcend reality and its restrictions. This had the effect of making Italian imperialism much more aggressive than prior Italian precedents, which were already quite ambitious. The Ethiopian War was emblematic of this new aggressiveness and assertiveness. One of the key tenets of Fascist ideology was that the new state was the reincarnation of the old Roman empire and one of the lessons of history was that power favored the bold. A daring attack and strike outwards into the Mediterranean would allow Italy to make this ideological picture a reality. Given that administrative anarchy bureaucratic dysfunction were the hallmarks of the fascist state, these sorts of ideas operated in an echo chamber which minimized any voices calling out for peace on the firm basis that Italy could not win a major war and would only become a subordinate to Germany.

Although Mussolini became Germany's sole ally in 1940, a crucial factor at play was Mussolini saw Italian belligerency as a means to transform Italy into a counterbalance to German hegemony within Western Europe. By eliminating the British and French presence within the Mediterranean when they were preoccupied with Germany, Mussolini felt that he could carve out a a large Italian sphere of influence in North Africa, the Balkans, and, eventually, the Levant. While this was done through the assistance of Germany, Mussolini conceived of entering in the war as escaping the shadow of his ally north of the Alps. One interpretation of Mussolini's aggressive foreign policy of the 1930s was that both he felt increasingly overwhelmed and sidelined by the ascendency of Hitler and Nazi Germany. Adventures like Ethiopia, intervention in Spain, his chaotic foreign policy at Munich were attempts by Mussolini to reassert control and regain the European spotlight he had enjoyed during the 1920s when fascism first made its name known. France's inevitable collapse, and Britain's strategic retreat made it seem like the golden opportunity for Mussolini to carve out a southern counterbalance to Germany's control over the northern and western Europe.

The problem with "a weight on the scales" from a military perspective was that it required a military that could act quickly and decisively. This was a tall order for the Italian Army, where motorization was tied to the anemic and protected Italian auto industry. Moreover, Mussolini often pushed operations far in advance of their timetable, so Italian generals had to improvise. The invasion of southern France was a rush job to take advantage of French weakness and it predictably ended with high Italian casualties for little gain. The disastrous invasion of Greece was another example of a premature operation that failed. The Italian Chief of Staffs had been working on a limited offensive invasion of Greece, Esigenza G, but Mussolini expanded the scope of the operation to a full-blown invasion. He additionally moved forward the initial timetable for Esigenza G, which shocked a the army chiefs. When the designated commander for Esigenza G, General Sebastiano Visconti Prasca, informed Marshal Pietro Badoglio about the operation, the Italian military chief thought the plan was madness. Not only was the weather inopportune, but Badoglio appreciated the difficulties of terrain and that taking the whole of Greece was likely beyond the forces detailed for the operation. When Esigenza G predictably failed, and Mussolini replaced Visconti Prasca with Ubaldo Soddu, who was arguably one of the most incompetent generals of the entire war. One of the rumors about Soddu was that while the Albanian front collapsed, he spent his evenings composing film scores.

Uboldo and Visconti-Prasca were symptoms of a wider rot within the Italian military establishment under Fascism. The latter general was typical of the type of officer promoted under Fascism; he was a natural sycophant to Mussolini and tried to adapt operations around Fascist ideals of action being able to transcend obstacles logic said were insurmountable. Ciano's diaries indicated that Visconti-Prasca was itching to be the conqueror of Greece and that he agreed with Mussolini that an aggressive coup de main would cause the Greeks to collapse. Soddu was likewise one of Mussolini's creatures within the Italian military establishment and knew loyalty to il Duce was part of his military portfolio. The promotion of officers based on political merits created a dangerous combination in that they were keen on fulfilling Mussolini's directives but lacked the military acumen to carry these already unsound moves out.