You're kinda describing how, for myself, I fit the 80s War of the Worlds television series into Star Trek. Even the post-apocalyptic second season; that all gets lost in the memory of the Eugenics Wars.
Except the two seasons don't even fit with each other, since season 1 posited that most people had forgotten the invasion already due to denial and a nebulously defined amnesia effect of alien contact (which was tied into the "alien abduction" mythos, and is obviously incompatible with the Trek universe), while season 2 retconned things to show, as you say, a post-apocalyptic world still in ruins from the 1953 attack. (Season 1 never explained how people justified the global devastation to themselves if they didn't remember why it happened, or how they managed to erase every trace of it in just 35 years.)
The last season 1 episode established that a second wave of invaders would be coming in four years, and I was inclined to assume that season 2 was four years later and the change was due to all the damage the aliens had done in the meantime. But that was, of course, impossible to reconcile with the female lead's teenage daughter still being only a year older in season 2.
Of course,
Alien Nation had its own internal continuity issues, retconning itself as it went. The alien slaves' Overseers were treated in the pilot as a deep dark secret that the Newcomers didn't remember because they'd been drugged on the slave ship, and the secret of the Overseers' existence was the catalyst for the pilot's entire plot; but the rest of the season ignored that and established that the slaves on the ship had been very aware of the Overseers, and that their existence was known to the Earth authorities right after the crash but they couldn't be prosecuted for crimes committed in space. But then the revival movies changed it so that many Overseers had been tried and convicted and shunted into an Operation Paperclip-type program to create advanced tech for the government. And that's on top of the revival movies decanonizing the season finale so they could redo its cliffhanger from scratch four years later, and altering the timeline of the Newcomers' arrival. And the business where you had Newcomer prostitutes servicing human clients in an early episode, but the second movie established that the two species needed a 6-week intensive training course to learn how to have sex without injury.
But at least
Alien Nation was a good series, as good as
Star Trek and with the same spirit of social commentary. WotW had an entertaining cast in its first season (before the season 2 producers dropped both the nonwhite regulars and replaced them with the walking mannequin known as Adrian Paul, and stripped the remaining regulars of any interesting personality traits), but it was pretty badly written (largely by scabs during the '88 writers' strike) and it had startlingly cheap production values compared to its syndication partner ST:TNG. When I revisited season 1 some years back, I was startled by how bad it was, since I remembered liking it for its cast chemistry. But even the actors were weaker than I remembered.
) But then you run into the things 
