On August 25, 1914 German soldiers set deliberately fire to the University Library of Leuven. 230.000 volumes were lost on that day including medieval and Renaissance manuscripts as well as more than 1.000 incunabula. The library building was rebuilt after WWI but put on fire again in WWII. That time more than 1.000.000 books were lost to the flames.
Lest we forget.
(For more on WWI you might check out the art project that filled most of my 2014 and brought together a network of friends all around the planet: From Berlin With Love.)