It should be the aim of grand strategy to discover and pierce the Achilles' heel of the opposing government's power to make war. Strategy, in turn, should seek to penetrate a joint in the harness of the opposing forces. To apply one's strength where the opponent is strong weakens oneself disproportionately to the effect attained. To strike with strong effect, one must strike at weakness.
B. H. Liddell HartThe most consistently successful commanders, when faced by an enemy in a position that was strong naturally or materially, have hardly ever tackled it in a direct way. And when, under pressure of circumstances, they have risked a direct attack, the result has commonly been to blot their record with a failure.
B. H. Liddell HartIn a campaign against more than one state or army, it is more fruitful to concentrate first against the weaker partner than to attempt the overthrow of the stronger in the belief that the latter's defeat will automatically involve the collapse of the others.
B. H. Liddell Hart