An armistice between the warring parties took effect on the 11th of November 1918. America and its allies commemorated the date as Armistice Day for a couple of decades, until it became clear that the "war to end all wars" had done nothing of the sort. In fact, as has almost always happened in the history of man's wars, the First World War solved nothing, and in fact planted the seeds of conflict that would germinate into an even greater World War in less than a generation. Following that war, politicians eager to curry favor with the generation that fought it (I know, I'm feeling terribly cynical this morning), established the 11th of November as Veterans Day. As opposed to Memorial Day, a commemoration of the war dead that began as Decoration Day and was initiated by the fair ladies of Columbus, Mississippi at Friendship Cemetery in 1865 (yankees hate this and claim a northern town as the origin--grist for yet another post), Veterans Day was designed to honor the living veterans of America's wars.
It has always bothered me that Americans don't seem to understand the difference.