Making strategy is a rational process: an objective analysis of how much power one has, and how much power one's competitors and rivals have, determines which ends are feasible. Strategists make mistakes, of course. Their assessment of the environment can be wrong, they can misread the strategies of the other players and under- or overestimate their resources, they can fail themselves to commit the resources required and implement what they decided. Or they can be outwitted by the strategists of another state. If the premises of a strategy turn out to be false, or a competitor or rival is more successful, strategy must be revised through the same rational process. ‘But governments and people do not always take rational decisions. Sometimes they take mad decisions, or one set of people get control who compel all others to obey and aid them in folly’, Churchill points out. History is full of examples of leaders who allowed religion, ideology or emotion to trump reason, overreached, and failed.

Philip II, Catholic King of Spain from 1556 to 1598, trusted in divine providence rather than heeding his advisors who warned of the lack of resources to make war simultaneously on protestant England, the rebellious protestant provinces of the Netherlands, and the ‘infidel’ Ottoman Empire. The results of this overreach were dramatic. The Spanish armada sent against England was sunk in the Channel (1588). The northern Netherlands, the United Provinces, became an independent republic and a great power, and would enjoy a ‘golden century’ (not least thanks to the influx of refugees and wealth from what remained of the Spanish Netherlands on the territory of current-day Belgium, I cannot refrain from pointing out). The Ottoman conquests were but briefly delayed before the empire continued its expansion.

Truly catastrophic was the result of Hitler's decision to invade the Soviet Union, after having failed to defeat the UK. Launching operation Barbarossa (22 June 1941) was logical within Hitler's own ideologically determined worldview; the destruction of bolshevism had been his avowed aim since the publication of Mein Kampf in 1925. But the decision was not rational when looking at the reality of a two-front war and the limits on German resources.