The Mongols used psychological warfare extremely successfully in many of their battles, especially in terms of spreading terror and fear to towns and cities. They often offered an opportunity for the enemy to surrender and pay tribute, instead of having their city ransacked and destroyed. They knew that sedentary populations were not free to flee danger as were nomad populations, and that the destruction of their cities was the worst loss a sedentary population could experience. When cities accepted the offer, they were spared, but were required to support the conquering Mongol army with manpower, supplies, and other services.