Well of course the main reason was expansion of political and regional power. When Mussolini became the Prime Minister, and dictator, of Italy, he attacked several countries, and the League of Nations did almost nothing about it. Seeing the world's idle reaction to Italy's conquests, Japan started expanding into the Asian Mainland and withdrew from the League of Nations under Emperor Hirohito. After all this, the world still did very little to stop these countries because they didn't want a second World War. Then Germany saw what happened and Hitler went and conquered many countries after withdrawing also from the League of Nations.
What does it say in your textbook?
Xpansion, Location and Domination.......!
Myself having been born in Communist East Germany in 1949, 4 years after the end of WWII, I developed a quite intense interest in this topic. I can give you a somewhat general explanation of the factors that lead to the rise of Fascism in Germany. Some historians would agree that the causes of German aggression go back to WW1. That war also ended with the defeat of Germany. The Treaty of Versailles which the Germans had to sign was considered by Hitler to be a humiliation that he intended to avenge. Also the Great Worldwide Economic Depression of the mid 1930s motivated the discontent of many people. Hitler took advantage of that and promised the Germans that he would restore their former glory. He did keep the promise when he came to power by helping to stimulate industrial and military production. Thus giving many Germans badly needed jobs. Of course he did have his own political ambitions also. Which were to regain the territory that was taken from Germany after WW1. This he did. Unfortunately he did not stop while he could have. History tells us that he went on to attack Poland, and then France, and England. Then Russia too. The rest is written in blood.