It's long been thought that humans hunted woolly mammoths to extinction. Anthropogenic global hunting, as it were. Or that a cataclysmic event did the trick.
It may be neither of those and just simple genetics.
DNA lifted from the bones, teeth, and tusks of the extinct mammoths revealed a “genetic signature” of a range expansion after the last interglacial period. After the mammoths’ migration, the population apparently leveled off, and one of two lineages died out.
They don't think these guys did it any more