Looking for any book recommendations on the history of China from the First Opium War until the end of the cultural revolution. I'm particularly interested in anything on the political development of China, how it developed a more cohesive national identity, how it modernized, how it adapted to a more expanded world view and the arrival of foreign concepts and ideas.

More specifically, I would love to find more information (be it books, essays or anything at all) on the war lord's period, or really just anything from the revolution of 1911 until the war with Japan. Most of the books I have found on this era are out of print and/or ludicrously overpriced.