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 <i>Titanic </i>to the explosions of the space shuttles <i>Challenger</i> and <i>Columbia.</i> Here are deadly train wrecks and airplane collisions, the great fires that destroyed London and Chicago, the Johnstown Flood, the crash of the <i>Hindenburg,</i> the nuclear accidents at Chernobyl and Fukushima-and many more historic calamities.