When Katniss refers to her ancestors she is talking about us. What has happened to North America/ how might we have contributed to the destruction of it?

We aew never apprised of what happened in the years before Panem. What we are told is that there has been an influx of storms, rising levels of ocean water, droughts and fires. We also learn that a lack of natural resources has caused wars within the continent. From this, we can infer that Collins is possibly looking at the result of global warming.