If we trace Buddhism back to its historical, Theravadan roots, we find that it is a practice of investigation. Buddhism is a practice that teaches one to analyze the world. The mind is settled and honed to a sharp edge, and then it penetrates through our experiences of reality to find the truth hidden at the core.
When Buddhism left India to China, it found a different culture. In India, there was a tradition of begging holy men, who could live in the forest and meditate all day, and then beg for alms. In China, no such structure was in place. Monks, like everyone else, had to work.
China was also the ancestor of Taoism. Taoism is a tradition of unification. Its inner workings are an alchemy, a uniting of seemingly diverse elements into a whole. Taoist writings describe creation as a series of steps that involve splitting off into many parts. From the great Ancestor, the Tao itself, arose yin and yang, the five elements, and eventually, the 10,000 things of the world. To reach the Tao, then, one simply reverses this process.
When the analytical Buddhism met the harmonizing Taoism, there was a new practice called Chan or Zen. Zen has a different flavor from both Taoism and Buddhism, yet it is intimately related to both.