"After World War One (1914-1918) many countries struggled to pay their war debts and reparations as Europe began to rebuild. This caused economic problems in many countries, as Europe struggled to pay war debts and reparations.”
http://economics.about.com/od/recessions/a/greatdepression_2.htm
The Aftermath of World War I
World War 1 was important to the world's history, you know about World War 2, but what was in World War 1? The US president wanted the nations to form a group of nations to prevent wars. The war caused the Germans to lose much territory and most of their power.
The causes of World War 2 and communism were mainly because of WWI. WWI began communism in 1917 when the Russian government weaken by war and people starving, a rebellion broke out. The war was between the whites as they called themselves and the reds. The whites were the government and the reds were the rebellion forces. The war was won by the reds and they establish a communist government.
The war left Germany in a deep financial crisis. They burned money rather than buy firewood because money was worth little value. Hitler took advantage of this, with the new government failing he overthrew the government and setup his Nazis party and he started a secret police and stop all opposing parties. Soon it led to World War II
The war also started countries like Poland and Ukraine and others. It broke up Austria-Hungary into several countries such as the Czech Republic and Austria. Russia or the Soviet Union as it was called lost much land. Its land formed countries like Poland. The Soviet Union gave up land to Germany before the war ended and those land were formed into individual countries after World War 1 ended.
It was an economic slump, there were many reasons but mainly people lost money biig time and had to do many repairs because of world war one that was why it was the longest and the worst depression ever experienced."The United States had emerged from the war as the major creditor and financier of postwar Europe, whose national economies had been greatly weakened by the war itself, by war debts, and, in the case of Germany and other defeated nations, by the need to pay war reparations." There are percentages and more info in all my links. It's a lot to read, I’m procrastinator so there's no way in hell I'm giving you facts. But I tend to not want to lean on Wikipedia so yeah... these three mainly have the three large reasons the great depression began in the first place.