The expansion

of the bureaucracy of government at this time allowed for feasible equipping, feeding, training and deployment of much larger armies. This changed warfare from an occupation of the ruling class to a professional activity undertaken by professional soldiers and officers. New specialist skills, such as engineering, signals, and mapmaking became viable occupations for these career soldiers. Sun Tzu was the most famous of these; a brilliant tactician and strategist, whose work The Art of War, which was written around 350 BC, is said to have influenced Mao Tse-Tung, and remains a standard text for military officers, as well as being widely read by ambitious people in other walks of life.