The Colossal Collapse

To avoid the Freedom Gangs, law-abiding citizens resorted to campsites far away from the cities, towns and suburbs. If you stay in your house despite having no electricity or gas, the Freedom Gangs will still break in and rob you. They will strip the copper wire clean from the walls, take anything metallic, and even if there isn't any electricity, they will grab your appliances.
They call themselves the Freedom Gangs because the Colossal Collapse has neither no law nor police to stop them from committing their crimes. Giving them the freedom to rampage their desires. A gang member will state that if there is no law, therefore, he is not committing a crime. The gangs call this era other names; Total Freedom or Absolute Opportunity.
Those who knew the Colossal Collapse was imminent had stocked up well, both on food and guns and with plenty of ammunition to spare. To their shock and horror, the Freedom Gangs wore special armoured suits that made those weapons obsolete. Blasting away rounds after rounds at the assailant only to find he just keeps walking towards you and knocks you out cold.
How the gangs got these high-tech suits that even the military and authorities never obtained is a mystery.
Their once-safe homes now remain derelict and an easy target which drove good obedient citizens to hide in the forests. By not having anything of value, albeit food and guns, the citizens thought they were now safe from the gangs.
Until one day, a robotic dog with a large mounted machine gun had gunned down the campers. The campers' guns were pointless, and once all the adults were dead, the gangs took the one most valuable possession; the children.