History has shown that Britain made a huge mistake by going to war with Germany for a second time in the 20th Century, losing its empire and reducing it to a third rate economic power. With WW1, it had to dust off a 100 year old international treaty recognizing Belgium's independence as an excuse to declare war and ruin its economy.
With WW2, Britain hastily put together a mutual defense treaty with Poland only a week before Poland was invaded by Germany (and the USSR), It then used this treaty as an excuse to declare war, even though Germany posed absolutely no threat to it. Once again, Britain claimed a pyrrhic victory over Germany while losing the rest of its empire and condemning Eastern Europe to Soviet domination for decades. Why did this happen? What was Britain's national interest in Poland?
German pre-war territory in Western Europe had already been restored, and Austria had willingly joined with Germany. The only German territory remaining in dispute was in the newly created states of Czechoslovakia and Poland. Czechoslovakia had never been a recognized entity prior to WW1, and it was already starting to break apart by the time Germany reclaimed the German areas of that country. As with the other territorial reacquisitions, Britain lodged some formal protests but did nothing to prevent them. British PM Neville Chamberlain claimed to have negotiated a big "peace" deal in Munich with Hitler, but it ended up being a feeble attempt at appeasement..
Then came Poland, which had been recreated after WW1 as an obstacle to German and Russian hegemony in Eastern Europe. Not only did it invalidate the borders agreed to by both countries the war, it also cut off Germany's largest and most important province (East Prussia) from the rest of the country. Germany wanted to restore a secure road and rail connection between them, as well as the formerly German city of Danzig which was along this route. Still smarting from public disparagement of his peace deal, Chamberlain urged Poland to reject any German proposals and then pledged that Britain would prevent any German incursions into its territory. When this happened in September 1939, his hollow assurances were exposed and he had to declare war on Germany to save face. Notably, he did not feel there was any reason to declare war on the Soviet Union, which invaded Poland from the east two weeks later! The Soviets also invaded Finland, and Chamberlain still felt there was no reason to declare war on them.
Other than some skirmishes involving British and German naval units, nothing much happened for the next six months. By then, Chamberlain was under increasing pressure to resign for getting Britain into another war with Germany. Yet in March 1940 he started bombing German naval facilities and laying plans to occupy Norway. The Germans got wind of these plans and acted first to protect their iron ore shipments from that country, also gaining permission to protect its shipping lanes around Denmark.
After futile attempts to arrange a peace agreement with Britain and France, who had deployed a huge standing army on its border, Germany invaded the latter in May 1940. Faced with this unfolding debacle, Chamberlain finally resigned and was replaced as Prime Minister by Winston Churchill. Churchill had maintained a hatred of Germany ever since he was removed as First Lord of the Admiralty because of his poor performance during WW1. Upon his appointment as PM, he began a campaign of bombing German cities and killing their inhabitants.
By the end of WW2 Britain was no longer "Great" and was already losing its influence in world affairs. As the ensuing 80 years have shown, it is no longer dominant even in European affairs. It seems that the decline of the British Empire weighs heavily on the shoulders of its two wartime Prime Ministers: The first motivated by spite, and the second motivated by malice against Germany.*
*It should be noted that subsequent German atrocities during WW2 were not known and played no part in Britain's declaration and prosecution of war against Germany.
