Hi, I'm John Green, this is Crash Course World History, and today's video is kind of a response to one of the most riveting history books you'll ever read, The Columbian Exchange by David Crosby. He had a good year in 1969, published The Columbian Exchange, played Woodstock, he was still on his first liver, what, it was Albert Crosby? Gosh, history never being as interesting as I want it to be. Right, so it was Alfred Crosby Jr., and in that book he wrote, The big questions are really the only ones worth considering, and colossal nerve has always been a prerequisite for such consideration. I love it! Before 1492, we couldn't really talk about a world history at all, we could only talk about the different histories of separate regions, but Columbus changed all of that, and everything else. The Columbian Exchange irrevocably homogenized the world's biological landscape.