Crash Course Community Questions Crash Course World History John Green teaches you the history of the world in 42 episodes of Crash Course. Learn, study and understand all the important civilizations, empires, wars, and revolutions the world has seen so far. Crash Course Biology and Ecology Crash Course Chemistry It's time to jump into Chemistry with Hank Green. He's been a life long lover of this subject and it's not just because of the rules, laws, bonds, and coefficients. But, also because of the men and women who shaped this science that deepened our understanding of our world so magnificently.