Plenty of history here!
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This timeline goes over all the major events and plot points of the saga, from before Half-Life 1 to the end of Half-Life 2. The HL1 manual indicates that the Black Mesa incident occurred on May 5, 200-, implying by the “-” that the incident could take place during any year during the decade. For simplicity’s sake, I assumed it happened in the year 2000 and went from there.