The common factor that led to aggression by these three countries was unhappiness with the status quo. All three countries felt that they were being treated badly in the years after World War I ended.
Germany had, of course, lost that war. In the peace treaty, Germany was treated very severely by the Allies. It had a great deal of territory taken away and was punished in many other ways that reduced its national pride. The punishments also hurt its economy. These factors made Germans want revenge. This desire helped fuel Hitler’s rise to power and it made Germans support his aggressive actions.
With Italy and Japan, the situation was different. Both countries had been on the winning side in WWI. However, both countries also felt they were not sufficiently respected by the international community. The Japanese thought they deserved a larger empire than they were being allowed to have in East Asia. Italy felt it had not been given as much territory as it deserved in the Treaty of Versailles.
Thus, all three countries felt aggrieved by the status quo and acted aggressively to change that status quo in the 1930s.
Japan, Germany, and Italy became aggressive nations in the 1930s. There are reasons why each country became aggressive.
Japan became aggressive for a few reasons. Japan was in desperate need of resources. They had very few resources within their country. They wanted to invade neighboring countries to get the resources they needed. The Japanese were also unhappy with some of the agreements made at the Washington Naval Conference. They were upset with the Five-Power Naval Limitation Treaty that allowed Japan to have three warships for the every five warships Great Britain and the United States had.
Germany became aggressive for several reasons. Germans were very bitter with the Versailles Treaty. They felt the treaty really treated them poorly. They resented have to accept the responsibility for the start of World War I. They were upset at the economic depression that resulted in part because of the heavy reparations they had to pay to the Allies. Germany was looking for revenge in the 1930s. Germany also wanted more land and colonies to control. War was one way to achieve these goals.
Italy was also upset with the Versailles Treaty. They believed they were going to get more land from the treaty than they actually received. Mussolini came to power and vowed to return Italy to golden days of the Roman Empire. Italy wanted more land to control, and the power that came with it. All of these countries had reasons for becoming aggressive.
The aggression by Japan, Germany and Italy in the 1930s was a result of their perception of Treaty of Versailles, an event that marked the end of World War I. All these states felt that they were treated unfairly and this is what led to unrest and aggression and, ultimately, World War II.
Germany, the most powerful and most advanced nation, was the biggest victim of the treaty following its defeat in the war. The treaty penalized Germany heavily, disbanded the army and prohibited the formation of a new army, removed any offensive capability and distributed all its colonies among the Allied Powers. This humiliation led to widespread opposition to the treaty and status quo, feelings that were used and manipulated by Hitler in his rise to the pinnacle of government.
Japan and Italy were dissatisfied. Japan wanted more power within Asia, while Italy wanted more in Europe. And this dissatisfaction and discontent caused the aggression of the 1930s and ultimately World War II.