Ah this should be easy.
1: After the First World War where the death toll (at the time) was inconcievable, people (as in everyone) did not want a repeat of it. As such they were prepared to resolve any and every problem with negotiation. They didn't want war, no-one did. Except the Germans, and they had a fucking good reason to go to war as well. They got absolutely raped (literally) by the Versailles treaty which was incredibly harsh. As such there was huge resentment in Germany towards the Allied nations, specifically France, and this leads me nicely onto point 2.
2: No matter what the Allies (UK, Russia, US, France etc) would have done, war would have broken out. And Germany would probably have done just as well even if the Allies did a pre-emptive strike. No matter what you think, the fact is the German army at that time was the most powerfull, best trained and most up-to-date army in the world. Nothing would have stopped their Blitzkrieg since no-one had seen that tactic used en-masse before.
3: "The West" did not sit around and do nothing until the cost was enormous. The US sat around and did nothing until the cost was enormous. If "the west" did nothing, then hell, the whole of Europe would now be under Nazi control.
5: No-one "let" the Nazis kill 6 million jews and capture most of western Europe. In case you didnt notice, at the time that the jews were being killed and western europe was being taken over, there were battles going on. People dying to stop the Nazis succeed in their mission.
4: I have no bias towards Christianity or Islam. I'm merely looking at the people who have the power. If I'm not mistaken, the world has to worry a lot more about President Bush and Tony Blair than "Al Queada". Suprise suprise Bush and Blair are both Christian. Hence my chuckling at your statement.
5: Doubtless you'll say terrorism is a big problem etc etc. Well hey, you are NEVER going to get rid of "terrorists". The fact is the West calls them terrorists whilst other people call the freedom fighters. And to be honest, if there was a Palestinian and an Israeli having an argument, i'd side with the Palestinian, but hey thats another debate entirely.
But all in all, i will probably wait for the reply you'll doubtless post with great anticipation to see what more sweeping, and frankly, idiotic statements you can come up with. I won't reply yo your post mind you as it is a tiresome waste of time since you seem unwilling to figure things out for yourself, and i really don't have the energy to waste.