Nature's disasters may be horrifying, but the calamities caused by man, which could have been prevented, are even more tragic. Now TIME tells the full story of history's most memorable man-made disasters, from the sinking of the Titanic to the explosions of the space shuttles Challenger and Columbia. Here are deadly train wrecks and airplane collisions, the great fires that destroyed London and Chicago, the Johnstown Flood, the crash of the Hindenburg, the nuclear accidents at Chernobyl and Fukushima-and many more historic calamities.