I think Japan attacking America had just a little something to do with America entering WWII... Quite frankly America was more than happy to see Britain fall to Nazi Germany until it wasn't in their best interests. Britain did pretty damn good defending itself against a power like Nazi Germany, not a single German soldier stepped foot on British soil and that was thanks to the British Army. I won't sit here and discredit America, obviously their part in WWII swung the power of balance but to suggest Britain came "begging" for help is a ludicrous suggestion. Don't act like you did us a favour, America realised Britain falling to Germany wouldn't be good for them.
Now, if I can cast your mind back to Iraq, George Bush's exact words to Britain and other nations was that they were either with him (aka go to war) or against him. It was a desperate plea and I've got no doubts that Obama will make the very same plea when the battle lines are drawn against North Korea and Iran. My point is, the British people are sick of being dragged into wars like that. We have no problem with Iran or North Korea, nor did we with Iraq, in fact there were many riots and protests over declaring war. We also have no problem in standing by America in wars when we believe that there is just cause to send our brothers, sisters, friends, fathers, sons etc into battle. There is no just cause here, not yet, nor do the majority think we have any right to tell another nation what it can and can't do when what we say it can't do, we do ourselves.