We did this to ourselves. What we are experiencing now, and what we will experience in the future is a self-inflicted wound. A deadly, self-inflicted wound. Like the one described in Revelation 13.
Should the Lord delay His Return and another civilization rise and replace our own, future historians will have a host of reasons to choose from. But, just like the fall of every other empire, the ultimate cause will be our own. We were corrupt, and that corruption killed us.
Worse, we sinned against God, and now… God is judging us.