RT Nick Szabo (@NickSzabo4)The coal is a great point. You can do steam engines with wood -- most of the trains in the American West of the mid-to-late 19th century were powered by wood -- but the Mediterranean core of the Roman Empire probably had considerably less forest than the 19th century U.S. Also as you point out the British had a unique local feedback loop; the earliest use of the steam engines was to drain the coal mines themselves. ...