The terrible amnesia to which humankind is prey is undoubtedly one of the principal causes of our inability to learn from history. The invasion of Occitania and particularly the massacre on 22nd July, 1209, of the 20,000 inhabitants of Béziers on the pretext that the town harboured 230 heretics whom the town council refused to hand over to the Crusaders, dramatically recalls similar events in modern times, such as the Spanish Civil War triggered in 1936 by Franco's army with the excuse of the Communist threat and the division of Spain, the invasion of Czechoslovakia in 1939 with the excuse of the Sudetenland, and the invasion of Poland by Hitler's German troops, in September 1939, over the question of Gdansk. More recently, we remember the wars in Vietnam (1958-1975), Afghanistan (2001), those launched in retaliation against the terrorist attacks of 11th September, and the Iraq war (2003) with the excuse of that country's supposed possession of weapons of mass destruction.
I endorse DJW's comment re the Peter Principle. It is, in fact, proven countless times every day, in every field of endeavour there is. The problem is that the PP was so obviously fitting for jokes on talk shows and in comedy acts, that the very true and serious nature of it was never really taken seriously when it was first published and hasn't been since other than by a few.