When genetic relatedness is reduced to small nuclear families (no tribes); when there is no effective cohesive ideology (e.g. religion, nationalism).
The predatory teenage male gang spontaneously forms and dominates, by sheer force.
(This situation prevails in some parts of Sub-Saharan Africa.)
When all else is stripped away the teenage male gang may dominate society.
The next step-up is organized crime - endemic gangsterism, piracy, robbery, extortion, blackmail etc.
Lacking extended families, tribes, clans - and lacking a cohesive ideology - this is the highest level of social organization that can be reached - the Big Man, mobster state.
My concern is that when the West collapses, this will be the level of society which will be dropped-down-to among the politically-correct, post-Christian indigenes - since Leftism has systematically subverted or destroyed all higher levels of social organization.