Alex Tabarrok reports on a couple of polling trends that explain a lot about how the public comes to support wars:

The public’s opinion of past wars improves as a new war approaches. Thus, after Vietnam most people thought the war was a mistake and this held true for decades until the beginning of the Iraq war when the opinion of war in Vietnam suddenly improved! Even more dramatically, a majority of people thought that World War I was a mistake until World War II approached when the percentage thinking it was a good war doubled. This is especially perverse in that any rational response has got to see WWI as a bigger mistake the more probable is WWII.

Althaus also shows, in Priming Patriots, that the intensity of new coverage typically increases support for war – regardless of whether the coverage is negative or positive.

When it comes to war, crowds don’t exhibit much wisdom.