Ah politics. The history books leave out more history than they tell.
In WW2 America was out placing embargos and patroling the seas in the Pacific making things difficult for Japan long before they attacked Pearl Harbor. In fact if any nation did to us what we were doing to them we would consider it an act of war.
They knew we were getting ready to go on the offensive, they had minimal resources and raw materials and were trying to expand into the mainland so they could actualy be a world contender (which obviously an Island the size of Japan could never be without expanding). They could see that while they were ahead, America had a much more vast number of resources, and would quickly catch up and exceed thier military capability in the coming years. So it was now or never.
They launched a strategic attack on a nation that had made it quite appearant it was an enemy of thier empire, and would go on the offensive once militarily ready. In thier shoes anyone that did not make the choice to attack then would have been a foolish military tactician. They managed to destroy a good chunk of our naval power with very few losses in a single blow. Had they waited until we were good and ready first we would have crushed them far more easily.
Our country was simply trying to remain openly passive until it could build a massive force without having bombs falling in the meantime. Keep in mind every nation that was actualy on the front lines was being bombed and had production severely hampered. If our factories were under constant attack we would not have faired as well either. We were simply fortunate that at that point in time we were an isolated untouched factory of a nation seperated by the rest of the world by large oceans.
So the front lines were kept elsewhere, the American public was made to think it was keeping out of the war and the world's problems while the leaders planned otherwise. Pearl Harbor was a rallying point, but had it not happened something else would have been used shortly thereafter.
America was involved in WW2 actively long before it officialy jumped in as documented for school children. It was both a friend and an enemy of those involved prior to then and the major players knew it and planned accordingly.
Everyone sacrificed a lot. America poured in lots of troops who lost thier lives, and was the unmolested factory for all the Allies involved in the war, producing goods that kept everyone else afloat. However America also didn't have soldiers on its streets, battles destroying cities, bombings of factories, bridges, power plants and supply lines etc. Much of Europe did, although the UK managed to keep thier fight in the skies and off thier soil.
America was also able to wait until the 8th round of a 12 round fight, when the other sides were bloodied and had beaten eachother into a stupor before pouring in to help save the day, in both world wars. So combined with no fighting on home soil, and attacking economies already struggling in the midst of war, they are successes to be proud of, but certainly not almighty enough to be rude to others who had not just thier soldiers on the front lines, but thier homes and families as well.
America has never had a modern war brought to it. We have never had bombs rain down on us, cities burning, and women and children killed by the millions along with our men. Not since the civil war have we had widespread horrors of war here.
The closest we have had is a mere couple buildings destroyed on 9/11, and that brought our economy to its knees for weeks. So lets not get too smug.
Call Brits a bunch of pansies for things they do now, like letting themselves be disarmed, not for combined valiant efforts we both took part in in our past.