TBH, the mass death in NA is mostly attributed to refugees and missionaries from Spanish-controlled Aztec lands entering into the Southwest, introducing new and exciting diseases from the conquistadors. Columbus was a piece of shit, yes, but that part likely wasn't him.

The issue is that we can't truly assign blame because there's so little information about what happened - due to their culture and materials available for construction (limestone sucks as a building material), many Plains and Eastern Native American sites (like Cahokia) just don't withstand the test of time, and an oral history means you're playing Telephone over the centuries. The plague idea has a little evidence to back it up (mass burial mounds make sense as crude plague control if you're in an area that prevents massive fires from being well controlled like the great forests of the Midwest and New England), but mostly it's based on educated guesswork and speculation more than anything else.