Legalism is even more concerned with law, order, and societal structure than Confucianism. While Confucianism eventually became both a political and a personal philosophy, I would say that Legalism is almost exclusively a political one, studied and followed by the ruling class as a guide to governance, but largely unknown to the general populace.

Legalism was also discredited (though never completely) during the Han dynasty due to its association with the brutal and tyrannical Qin dynasty.

In the novel, Cao Cao definitely had a Legalist undercurrent to his words and actions which is why he is painted as a villain, while Liu Bei was held up as a Confucian exemplar in contrast.