Alright kiddo, let me try to explain the events that happened before World War II in Europe to you.
After World War I, many European countries were left devastated, and Germany was hit the hardest. The Treaty of Versailles, which ended the war, put all the blame on Germany for starting the war and made them pay huge sums of money in reparations. This made the German people very angry and frustrated with their government.
In the 1930s, a man named Adolf Hitler rose to power in Germany. He was a very charismatic leader and promised to make Germany great again. He blamed Jews and other minority groups for Germany's problems and began to persecute them. He also started to invade neighboring countries, which made other European countries very worried.
In 1938, Hitler tried to annex Austria, which was a neighboring country. He was able to do so because the leaders of Austria welcomed him. This made other countries even more worried because they saw that Hitler was expanding his territory.
Then in September 1939, Hitler invaded Poland. This was the final straw for other countries, and Britain and France declared war on Germany. This was the beginning of World War II.
So to summarize it for you, after World War I, Germany was blamed for the war and was made to pay huge amounts of money. In the 1930s, Hitler rose to power in Germany and began persecuting minority groups and invading neighboring countries. This ultimately led to World War II.