Originally, the concept was more a means to get to one of Blumhouse's classic home invasion plots, but as it's developed and grown writer/director/producer James DeMonaco has redefined the franchise to look more at the socio-political implications: why a government would really do this (clue: it's not about "unleashing the beast"), what would change around the world in the other 364 days, and how it reflects the current state of America.
He's also built a pretty coherent timeline of shocking events to boot. Related: The Purge Movies: How To Watch In Chronological Order From events now in our past through to disturbingly far into the future, here is the best timeline for The Purge that exists.
For the most part, the movies have been consistent in dating (Halloween Easter Eggs aside), with most avoiding presenting an actual year and instead placing themselves in the continuity only in relation to other films.
That means, while the technology in later installments may seem antiquated (although that could also be a commentary on the backward society), things mostly line up.Read more on screenrant.com