Someone send me the Cliff Notes :)
The Roman welfare state was off the charts. A citizen of Rome had everything for free. Eventually, the freed slaves and African immigrants were the majority and had no dog in the fight. Rome bred itself out, gave away assets to foreign citizens and collapsed from demographics.
This is written everywhere else but this guy takes the long way round.
His solution to collapse is to not fight against the forces that bring change. We have a problem, we expend large amounts of resources, money to fix it. This expending of energy is what causes collapse. Rome was under pressure within and from outside. They spent a lot of money, raised taxes, formed new legions, built fortifications. All a reaction to the pressures. Collapse.