On War by Carl von Clausewitz
Far more encompassing than I expected.
Kind-hearted people might of course think there was some ingenious way to disarm or defeat an enemy without too much bloodshed, and might imagine this is the true goal of the art of war. Pleasant as it sounds, it is a fallacy that must be exposed: war is such a dangerous business that the mistakes which come from kindness are the very worst.
Lastly, even the ultimate outcome of a war is not always to be regarded final. The defeated state often considers the outcome merely as a transitory evil, for which a remedy may still be found in political conditions at a later date.
From the enemy's character, from his institutions, the state of his affairs and his general situation, each side, using the laws of probability, forms an estimate of its opponent's likely course and acts accordingly.
Let us accompany a novice to the battlefield. As we approach the rumble of guns grows louder and alternates with the whir of connonballs, which begin to attract his attention. Shots begin to strike close around us. We hurry up teh slope where the commanding general is stationed with his large staff. Here connonballs and bursting shells are frequent, and life begins to seem more serious than the young man had imagined. Suddenly someone you know is wounded; then a shell falls among the staff You notice that some of teh officers act a little oddly; you yourself are not as steady and collected as you were: even the bravest can become slightly distracted. Now we enter the battle raging before us, still almost like a spectacle, and join teh nearest divisional commander. Shot is falling like hail, and the thunder of our own guns adds to the din. Forward to the brigadier, a soldier of acknowledged bravery, but he is careful to take cover behind a rise, a house or a clump of trees...
A little further we reach the firing line, where the infantry endures the hammering for hours with incredible steadfastness. The air is filled with hissing bullets that sound like a sharp crack if they pass close to one's head. For a final shock, the sight of men being killed and mutilated moves our pounding hearts to awe and pity.
Everything in war is very simple, but the simplest thing is difficult. The difficulties accumulate and end by producing a kind of friction that is inconceivable unless one has experienced war.
Habit hardens the body for great exertions, strengthens the heart in great peril, and fortifies judgment against first impressions. Habit breeds that priceless quality, calm, which, passing from hussar and rifleman up to the general himself, will lighten the commander's task.