The origins of the war lie in the unfinished business of the Great War, in Europe at least. Germany had been racked by political instability and economic problems throughout the 1920s. By 1933 Germans had voted for a new leader in Adolf Hitler. He set about transforming Germany into a National Socialist state dedicated to his ideals of racial purity and the extinction of communism.

Hitler's first step was to increase Germany's armed forces. For one thing, he did this to reduce the armies of unemployed workers in Germany. For another, the Disarmament Conference of 1932 had clearly shown that the other nations were not prepared to disarm.

In March 1936, Hitler took possibly his biggest ever risk by moving troops into the Rhineland area of Germany. The demilitarisation of the Rhineland was one of the terms of the Treaty of Versailles. It had also been confirmed in the Locarno treaties of 1925. It was a risky ploy but Hitler had chosen the time and the place well.

From the reoccupation of the Rhineland in 1936 onwards, Britain and France followed a policy of giving in to Hitler's demands. This policy became known as appeasement. For both the British and French, appeasement was also rooted in the horrific experiences of the First World War. The British and French people and their leaders did not want to see another generation wiped out by shells and machine-guns. Another factor behind appeasement was that Hitler was not the only concern of the western allies. If anything, they were more concerned about the spread of communism and particularly about the plans of the new leader in the USSR, Josef Stalin.

By 1937, Hitler, the dictators in Europe, and the Japanese government saw that they had much in common. Germany, Italy and Japan all signed the Anti-Comintern Pact, which was clearly aimed at Russia. The new Axis alliance took shape. With the successes of 1936 and 1937 to boost him, Hitler turned his attention to his homeland of Austria. The Austrian people were mainly German and, in Mein Kampf, Hitler had made it clear that he felt that the two states belonged together as one German nation. Hitler was confident that he could bring them together into a 'greater Germany'. German troops moved into Austria in March of 1938. The ‘Anschluss’ was complete through Hitler's decisive action.

Hitler now had designs on Czechoslovakia. When the new state was created by the Treaty of Versailles it included a large number of Germans in the Sudetenland area. The leader of the Nazis in the Sudetenland, Henlein, stirred up trouble among the Sudetenland Germans and they demanded to be part of Hitler's Germany. Europe seemed to be rumbling towards war. In a last ditch effort, British Prime Minister Chamberlain flew to meet Hitler in Munich on September 27 to see if war could be avoided. The following morning Chamberlain and Hitler published a joint declaration. Soon after the declaration German troops marched into the Sudetenland. At the same time Hungary and Poland helped themselves to large amounts of Czech territory. The Czechs had been betrayed, but the rest of Europe breathed a sigh of relief and Chamberlain received a hero's welcome back in Britain.

In all of the negotiations and frantic plane journeys, the largest factor in Chamberlain's mind was his dread of war. As he flew back and forth to talk to Hitler he could see how vulnerable Britain's towns and cities were to bombing. Chamberlain was also deeply aware that Hitler's rearmament programme had left Britain and France behind in 1938, not just in quantity but also in quality of up-to-date weapons and equipment. In Chamberlain's view, Britain was simply not ready for war. Perhaps Hitler had not been ready either, but nobody had called his bluff.

In September 1938, Hitler said, ‘The Sudetenland is the last problem that must be solved and that will be solved. It is the last territorial claim which I have to make in Europe.’ In March 1939, he showed that his promises were worthless. On March 15, German troops crossed into Czechoslovakia and were soon in Prague. It seemed that Hitler the gambler was at work again and that he had his sights set on further conquests in Eastern Europe. Chamberlain ordered conscription and warned Hitler that if he attacked Poland (the next target on Hitler's list) he would face war from Britain and France. Hitler ignored the warning.

Hitler's next target was the strip of German land in Poland known as the Polish corridor. His main concern, however, was the USSR. While he had convinced himself that the West would not fight, he was less sure about Stalin and the USSR. Stalin had explored the possibilities of an alliance with France and Britain in the 1930s, but the policy of appeasement seemed to be pointing Hitler towards him.

Stalin decided to ally with Hitler. On 24 August 1939 the two arch-enemies signed an agreement but they refused to give out any details of what the agreement contained. The agreement was quite simple. Hitler and Stalin agreed not to attack one another but they also agreed to divide Poland between them. Now fully confident, Hitler invaded Poland in September and Soviet forces attacked from the East. Poland soon fell, but to Hitler's surprise, Britain and France held to their promises and declared war on Germany. Hitler had taken one gamble too many.

However, it was a long time before it seemed that way to anyone. Hitler’s forces swept through much of Eastern Europe, then Scandinavia and on to France by the summer of 1940. Only the RAF prevented him invading Britain, but the new technology of air warfare was used to devastating effect. All of Britain’s major cities were pounded by the German air force.

Hitler’s first major error came in the summer of 1941 with the invasion of the USSR. By the winter of that year his forces were locked in a bitter struggle with the Red Army and the Russian winter. It was to be the Red Army which defeated Nazi Germany.

The USA also entered the war late in 1941. Rivalry between Japan and the USA had been growing since the 1920s. A group of powerful businessmen and military leaders wanted Japan to build an empire on the mainland of Asia. As the depression began to hit Japan, these expansionists took their chance with the invasion of Manchuria. These developments were watched with concern in America. The American President Roosevelt was especially concerned when Germany, Japan and Italy became partners in the Anti-Comintern Pact. In that same year Japan launched a full-scale invasion of China.

Japan wanted to carve out an empire in the Far East which would make it self-sufficient in vital materials such as rice, oil, coal and rubber. The problem was that this would threaten the USA. Japan also had a very large and powerful neighbour in the USSR. Hitler solved Japan's second problem when he invaded the USSR in June 1941. In July 1941 Japan took control of French Indo-China and it seemed that Japan had made up its mind to challenge the USA. Roosevelt froze Japanese assets and cut supplies of iron. This made Japan's leaders even more certain that they needed an Asian empire.

The tension grew. While fearsome battles raged between Germany and the USSR the Japanese laid their plans. Japan could not challenge the USA outright, so cunning was needed. Admiral Yamamoto devised a plan to knock out America's Pacific fleet in one swift blow. This would give Japan time to create its new empire. By the time the USA had recovered, Japan would be able to draw on the resources of its empire and the USA would be unable to do anything. On the morning of December 1941, some 300 planes took off from Japanese aircraft carriers to launch their attack on the US Pacific fleet at Pearl Harbor.

The USA and Japan were at war. It was to begin a wide ranging and bitter campaign that would end in the first and last use of nuclear weapons in war.