The second half of human development. Starting with the Golden Age of Exploration followed by the Industrial Revolutions (yes, there were two). After that comes the rapid urbanisation of America. Then after a brief intermission comes the World Wars, leading up to that one period of time when consumer goods popped up like baby rabbits. After that comes the modern-day introduction of equality and hopeful peace.
P.S. Can you spot the D.S. al Coda sign? I ran out of ideas on the last few sets, so I just made stuff that I like.