To add to what was already stated, and an important fact that is almost always overlooked when looking at 20th century Germany is that the United States kept the Weimar Republic afloat during the 1920s. The US was able to do this because they never actually signed the Treat of Versailles. By the mid 1920s the nation was well on the way to recovery. This was one of the major reasons that Hitler was not able to get a foothold during his Beer Hall Putsch.
However, when our economy crashed along with the stock market, we could no longer send money over to Germany. Without the American money, the Weimar quickly crumbled and Hitler was able to gain his foothold, and the rest, as they say, is history.
One of the major factors leading to the rise of authoritarian regimes in Europe after the end of World War I was the nature of the peace settlement concluded in the Treaty of Versailles. The treatment of Germany, which was stripped of crucial parts of its territory and made to pay reparations that destroyed the German economy and led to hyperinflation, resulted in a tremendous anger and resentment that fueled the rise of Hitler.
Although Italy was on the "winning" side in World War I, most Italians did not feel that they had been treated fairly in the settlement. The Italian army suffered devastating losses, and the Italians were not given some of the territory they had been promised. Even worse, Italy, which had only been unified in 1861, was fragile politically, with strong anarchist and socialist movements, and in bad economic shape, setting the ground for the rise of Fascism as a nationalistic "law and order" party, with Mussolini famously claiming that he would make the trains run on time.
The Spanish Civil War, which culminated in the dictatorship of Franco, was due more to internal political dynamics than to a reaction to the European situation. Right wing leaders, wealthy elites, and the Roman Catholic Church were worried by the election of the Popular Front, a left-wing government, and staged a military coup. Hitler and Mussolini, worried about the power balance in Europe, gave some support to Franco, hoping to keep Spain neutral in future conflicts.
Russian losses in World War I, as well as economic problems, especially mistreatment of peasants and deep distrust of the Tsar, his wife, and Rasputin, gave popular support to the Russian Revolution. In many ways, though, despite its late date, the Russian Revolution was not really parallel to the rise of fascism, but rather should be seen as a delayed version of the earlier eighteenth- and nineteenth-century movements such as the American Revolution and French Revolution, aiming to break the power of a corrupt aristocratic regime.
The rise of right wing authoritarian regimes in Europe after WWI was one of the major causes of WWII. This rise was caused largely by discontent in various European countries. This discontent was felt mainly in countries that were unhappy with the provisions of the peace treaties after WWI. It was also felt by those who were threatened by various changes that were going on in Europe at that time.
The main cause of discontent that led to the rise of right wing authoritarian government was unhappiness with the treaties that ended WWI. This unhappiness was felt in Italy, which wanted more territory as a reward for having been on the winning side in the war. It was felt in countries in Eastern Europe that felt that they had not been given all of the territory that should have been theirs. It was felt, most especially, by Germany, which felt that it was being horribly abused by the terms of the Treaty of Versailles. These countries wanted someone who would promise to get what they felt was their due. The right wing authoritarians seemed to have a way to accomplish this and so they were able to gain in popularity in many European countries.
People also turned to right wing authoritarian governments because of their concern with changes that were going on in Europe. The major change here was the rise of communism. The Bolshevik Revolution and the creation of the Soviet Union energized communists around Europe and those communists seemed like a real threat to many citizens of various countries. Economic changes, particularly once the Great Depression hit, were very worrisome to many people. Making these problems worse was the fact that the democratic governments did not really seem to be up to dealing with the social unrest brought about by these problems. People started to think that it would be better to have dictators who could rule with a much stronger hand than the democracies could. These right wing authoritarians promised a return to a more selfless, nationalist way of life that would make people feel that they were all united for the good of their country. This was very attractive at a time of change and at a time when people were unhappy with the ways in which their countries had been treated after WWI.