Adolf Hitler was the leader of the National Socialist Party in Germany, usually called the Nazi Party. He was an incredibly power-hungry and ruthless politician, and one of the most evil men of modern times. In fact, he seems to have had a talent for attracting evil, and for bringing out the evil in other people, as demonstrated by every high-ranking member of his Nazi Party, including Joseph Goebbels.
After the First World War, Germany was in a terrible state. Soldiers returning home from the trenches, having suffered just as much horror as British soldiers, not only faced the shame of their country's defeat, but found that the Allied Powers (Britain, France and Russia) had made Germany sign a peace agreement which was very unfair. This was called the Treaty of Versailles, and it stated that Germany was entirely to blame for World War One, and made them agree to pay money to the Allied Powers to make up for the damage done. The amount was 132 billion marks, which in today's money would be £284 billion. It was soon obvious that Germany couldn't make these payments. The German economy collapsed and people began to starve.
Adolf Hitler © Bundesarchiv
Adolf Hitler had fought on the side of Germany (he was actually Austrian, born in what was then Austro-Hungary) and he was understandably bitter about the way the country was treated. He decided he would make Germany great again, and build an empire that would last a thousand years. His vision was very appealing to the defeated German people.
Slowly and patiently, he began to build support for his ideas, and by 1930, the Nazi Party was the second largest party in the German Reichstag (similar to the House of Commons in Britain). Hitler now began to use terror tactics, sending squads of men to beat up members of opposition parties and cause chaos and destruction. Hitler and his men particularly targeted Jewish businesses and Jewish people - hatred of Jews is called anti-Semitism, and Hitler and the Nazis were deeply anti-Semitic.
By 1933, he was Chancellor of Germany (equivalent to Prime Minister). He immediately set about changing laws to give himself absolute power, and continued to use extreme violence, having people killed for daring to criticise his authority. Over the next six years, he revived the German economy, built up Germany's army and air force again, which was not allowed under the Treaty of Versailles, and took back some pieces of land where German people lived but which had been taken away and given to neighbouring countries under the Treaty. This made him popular in Germany, and there were plenty of people outside Germany who felt that the Treaty of Versailles had been too harsh, and Hitler was reasonable in breaking it.
By now, Hitler wasn't using such obvious terror tactics, except against Jews, some of whom fled Germany for Britain and America, leaving everything behind. Judith Kerr, who wrote The Tiger who came to Tea and the books about Mog the cat, was a child when she left with her family. She wrote a fantastic novel about it, called When Hitler stole Pink Rabbit.
Those Jews who stayed in Germany faced more and more discrimination, first losing their jobs and businesses, and later, being arrested and taken away, often in the night, by Nazi soldiers. As Hitler invaded more and more countries across Europe, the Jews in all those countries were rounded up. By 1942, midway through the war, Hitler and his henchmen had decided what to do with these innocent people: they put them on trains, crammed into cattle trucks, and sent them to concentration camps to be killed in huge numbers. This is what is called the Holocaust, and it's what happened to Anne Frank.
The Second World War continued until 1945. By April, Germany was in ruins after attacks by the Allies (the photograph of Dresden on Bomber Harris' page gives you an idea how bad it was), and Hitler realised he could not win. He retreated to a bunker in Berlin where he killed himself on 30 April 1945. Germany surrendered shortly after, on 8 May 1945.