Ahmm thats kind of hard to say because there are several massacres that can be the worse or be in the list of the most worse. For example: in South Korea there was a guy in 1982 who killed 56 people in several villages in the same night, The Port Arthur massacre in Australia commited by Martin Bryant in 1996 that killied 35 people there, then maybe the most recent by Anders Behring Breivik in Norway where died 75 people and if we are talking about school massacres then the one in 1927 by Andrew Phillip in the The Bath School at Michigan where he exploted 3 bombs that killed 45 people including students and the most recent is the Virginia Tech Massacre by Seung-Hui Cho where died 32
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The most terrifying fact about the universe is not that it is hostile but that it is indifferent; but if we can come to terms with this indifference and accept the challenges of life within the boundaries of death — however mutable man may be able to make them — our existence as a species can have genuine meaning and fulfillment. However vast the darkness, we must supply our own light