Adolf Hitler always wanted a wide-scale European war. But the war that broke out on August 31, 1939 wasn't the one he'd wanted. He had, not entirely quixotically, expected the Wehrmacht's invasion of Poland to result in another bout of appeasement from France and Great Britain. His resumé of crimes was already lengthy. He'd already violated the Treaty of Versailles and begun to re-arm on March 16, 1935. He'd already re-occupied the Rhineland on March 7, 1936. The Franco-British Stresa Front initiative had failed and the Anschluss, annexation of Austria, went ahead on March 12, 1938. France and Britain had abandoned Czechoslovakia and allowed the Sudetenland, and then the rest of the country, to fall into German hands. Why would things be different in Poland?
Say what you like about him, General Francisco Franco wasn't a fascist. He was a dyed-in-the-wool authoritarian conservative who was able to divide the peoples of Europe based on their inclination - left or right. Let us recall that Spain stayed neutral in the war, save for that division of undesirables and adventurers sent to crusade against Communism on the Eastern Front. Franco had good reason to want to fight Communism - the only government that had provided support to the Republic during the Spanish Civil War had been the Soviet Union. Britain and France had actually imposed an arms embargo on Spain. Meanwhile, Italy and Germany wasted no time in sending men and materials to their side. Middle-class and conservative opinion in Britain was too concerned about the advance of social revolution and Bolshevism in Iberia to save the Republic, although they didn't passionately identify with the Catholic Church that inspired General Franco.
As we all know, the Republic fell and Spain was kept out of European affairs for another thirty years. But both the fascists and the anti-fascists were confirmed in their contempt of the governments that had hidden behind the doctrines of 'non-intervention'. And, by the time the Republic had fallen in 1939, they were hardly persuaded to change their minds by events further east. The liberal democracies of Western Europe had continued to show their weakness of will, which contrasted unfavourably with the resolute determination of the fascists, and did not a little to hasten the spread of authoritarianism throughout Europe. The Munich Agreement brought personal shame to the signatories almost immediately, and Edouard Daladier is said to have muttered "Bande de cons!" ("Band of idiots!") when viewing the cheering crowds of Paris upon his return. These were the countries that had abandoned the Spanish Republic and now abandoned Czechoslovakia. And where was the Soviet Union in all this?
At the start of the 1930s, the Communist International (Comintern), mother of the little baby Communist parties outside the Soviet Union, had encouraged its charges to direct their fire against their most immediate political opponent - moderate socialists. But around 1934 the Soviets came to regard their most immediate enemy as fascism, and began to campaign actively for common action against it with the West. The West, however, still regarded the USSR as the main enemy, and not the fascists. Prior to the war, Nazi Germany was not viewed as such a great evil by common public opinion in the West. The Endöslung still looked likely to take the form of mass expulsion, and Germany appeared to be a flourishing country with a popular government. The ugly head of Bolshevism, meanwhile, reared large across Europe and threatened to destroy the existing order absolutely. National Socialism was surely a bulwark against this.
But how incredibly wrong these people were. Those who read Mein Kampf saw it first. The logic of Hitler's war would eventually drag the whole World into it, and the Soviet Union was forced to engage in a desparate rearguard action to try and delay this fact. The Molotov-Ribbentrop Pact of August 1939 was signed when Stalin knew that after four years of trying he could never enlist the support of the West, and so resigned himself to the factuality of German expansionism. In return for large portions of the land lost from the Russian Empire after the Revolution, he would agree not to attack Nazi Germany. He then hoped that Nazi Germany and the Allies would decimate each other, hence weakening both. The Allies were hoping that Soviet Russia and Nazi Germany would do a similar thing to each other, but were never ready to approach the Soviets to this end.
Hitler finally mobilised the mass of public opinion in Britain against fascism by the events of 1938 - 39, which made the policy of appeasement self-evidently absurd. The policy goals of Nazi Germany were irrational and unlimited, as the goals of totalitarianism always are. Britain had many reasons to avoid war - it wasn't just the people that feared it (horrible memories of the Great War still lingering for those who hadn't forged their entire self-identity as a frontsoldat, as the fascists had), but the government as well. Britain knew that the war would lead to the liquidation of its Empire, it could ill afford it, and it felt itself militarily unprepared. And let us remember that Winston Churchill was not anti-Italy, but he was not willing to allow the abberation of Nazi Germany to threaten what his country stood for. The events of 1938 - 39 had destroyed any notion of appeasement based on realpolitik (war was now inevitable), leaving the only logical opposition to war in those who saw National Socialism as the last rampart of the defence against Communism, and had hence abandoned the status quo anyway.
Chamberlain scattered assurances against German aggression around Eastern Europe without even informing the Soviets. The idea was to make a show of strength without having to actually exercise it, and even as Poland was carved up he was willing to negotiate. Hitler knew that the protection agreements were just waste paper and refused to negotiate, but he misjudged the reaction of the British and French governments. He had mobilised public opinion in Britain against himself too dramatically, and the statesmen of Britain and France were forced to declare war. Hence began the 'Phoney War', when the Brits and French weren't sure exactly what to do now they were actually at war. Then, in April to May of 1940, as Hitler smashed into the Low Countries and France, it became patently clear. Winston Churchill became British Prime Minister on the day of the invasion of France, Belgium, Luxembourg and the Netherlands, and there was no more room for appeasing anyone.