If you've read Jim Collin's other famous books "Good to Great" and "Built to Last", you are going to be disappointed with this one. Jim Collins resorts to his past methodology of pairing contrast companies to try to come up with answers on how mighty companies fall. According to Jim, the path to failure are the following five phases:
1) Hubris born of success
2) Undisciplined pursuit of more
3) Denial of risk and peril
4) Grasping for salvation
5) Capitulation to irrelevance or death
Now, this is probably something you could have picked up from the Bhagavad Gita. In fact, just to digress a bit, there's a lot of management stuff that can be picked up from the Bhagavad Gita. Where Jim falls short is to fail to explain conclusively how his research led to these conclusions.
If you haven't read Jim's earlier books, it's still worth a read. If you have, you won't miss much if you skip this one.