Security services have been warning us of inhouse terrorism for years. This is what we are seeing now.
The US for one could just stop their war on drugs, which has been ravaging the world for decades, and only has like 1% efficacy, and use that money in programs to prevent this. But unfortunately we no longer live in times where reason rules.
Zero-sum ideologies have taken over. We live in societies where other people’s gain are seen as our loss. And then what we get are huge society splits which will eventually and inevitably be the end of that society as it was.