Often times religion has had major effects on a society, big or small. The Tang and Song empires of China were no different. The renaissance of Confucianism or Neo-Confucianism, has had many positive and negative effects on the Tang and Song eras. Confucianism did not allow military power and most rulers at that time were Confucians and had to abide by these rules. Also, Confucianism focus was to find "the way" which was the pursuit of self discipline and building character. Again, most of the noble were Confucians and had to be less greedy. Both of these effected the cultures of the Tang and Song societies.
Confucians believed that war was not the way, and since the emperor and other nobles were Confucians, they had to abide by these rules. The emperors depended on uneducated peasants, the poor, mercenaries and their allies for malarial support. This would not be that effective against an attack from an enemy that my have a well trained army of thousands of men. Because the militaries of the Tang and Song empires were not very strong, they depended on diplomacy for peace. They would pay tribute to their enemies to avoid conflict. Because they had to pay tribute the empire could not grow as big as they should have been.
Neo-Confucianism's goal was to find "the way" which was the pursuit of discipline and self cultivation. Most of the noble men and rulers at this time were Confucians and followed these beliefs. Because they lived up to Confucian ideals, they could not be greedy or generally mean to others. This meant taxis and such unpleasant obligations would be kept to a minimum. This at first sounds good but in the long run, really isn't. It has both positive and negative effects.
The positive and negative effects of these two Confucian beliefs both helped and destroyed the empires of the Tang and the Song. Because the empire had a small army, they made themselves susceptible to military attack from enemies.