You are right CVC. I think one has to know what it's enemies capabilities, motives, and desires are and what they are willing to sacrafice to get those needs met. I'm not sure the example you refere to were done out of irrationality. In fact if you dig deeper you will find that these histroical events seemed very rational at the time.
We like to pat ourselves on the back for victory in WWI, but the bulk of the work had been done well before we arrived. Germany had fought the Common Wealth Forces much longer than they had fought us. By the time we joined in Germany was spent and simply holding ground.
The USA only became a superpower afterwards as a result of WWII. In the years between WWI and WWII noboby really feared the USA much. We had a very small military in those years that was still mainly horse drawn, many serviceman in those days were forced by a judge to join the military in leu of jail time for petty crimes, if that gives you any idea of what our forces were made up of at the time. When you really look at what had taken place up til Dec 7th and 8th of 1941 you can clearly see that Japan and Germany really had the upper hand and really struck genuine fear into the rest of the world. It took a total of 6 years (4 of those years we participated), billions of dollars, and hundreds of thousands of lives sacraficed to finally beat those two countries down and defeat them, and we didn't do it single handed either. But in the beginning nobody stood in Germany and Japans way.
Saddam was a friend to the USA in the 1970's and 1980's. We wined and dined him, funded him in his war with Iran. We needed him to defeat Iran. Our own government was in bed with Saddam right up until he invaded Kuwait. In the beginning Saddam honestly believed that the US would support his effort against against Kuwait. He wasn't initially trying to flex his muscles in front of us or trying to piss off the world. To Iraq it was a private dispute. Kuwait was really the one who set in motion the actions that Saddam took against them. They were pumping out oil from Iraqi soil and not paying Iraq a dime. He finally got sick of Kuwait trying to backrupt his country and he got sick of the underhanded bullying and condisending attitude the Kuwaiti royalty was displaying towards Iraq. Kuwait got taught a lesson, and well deserved too. But in the end we still could not let someone like Saddam control the worlds supply of oil.
As far as N Korea goes, don't know what to say about that. Only time will tell.