Homo sapien expansion after the last glacial maximum is a strong contender, but my understanding is that we don't yet have enough data to rule out environmental changes, or sufficient resolution to really prove it was us.

The most convincing argument I've heard points out that Africa - where we evolved - has more surviving mega-fauna than any other continent. If animals who had more evolutionary time to develop strategies for coping with humans are way more likely to survive, that strongly suggests we played a large role.

It's an area of ongoing research without a definitive answer though.