For quite a long time war was a simple affair: amass as many men as you can, arm them as heavily as you can, then hurl that snarling mass of sharp things and yelling bearded madmen at the enemy yelling bearded madmen. But somewhere along the way someone figured out they can do better. That hitting a weakened enemy line with cavalry in the right moment will cause the men there to disperse, which will wreak havoc in the enemy morale, which will cause their entire army to abandon the battle. And so military tactics was born.