Depends what you regard as "historic", Angel.
This "rivalry" with United was never a thing until the late seventies when they became very annoyed that despite the trophies they had started amassing, the media still regarded United as a much bigger and more glamorous club than them.
The jealousy the RS felt toward United back then was tangible.
From that period on and into the 80s they started developing a fanbase in the south and in Scandanavia and the "rivalry" began to be fuelled as those fans already in those areas whom had got into United during the post Munich sympathy wave suddenly had a rival set of fans to goad and this added oil to the fire.
Then along came Sky who decided to big this fixture up beyond any importance it has had during the EPL era.
Or any era comes to that.... I am a man in my 60s and I can count on one hand the amount of times Manchester United and Liverpool have been involved in a battle for the Title with each other in my football supporting life.
But only if I try real hard
I have stopped watching that fixture when it is on TV.....not only is it normally a borefest on the pitch, the atmosphere is usually very flat off it.
It is a manufactured rivalry without any rhyme or reason beyond Kopite envy and Sky hyperbole.
And now a couple of generations of fans have bought into it without actually knowing why
Now....I appreciate that a younger person than myself would have grown up knowing only about it in today's terms and that such a person would have a totally different perspective on what is historic as it might have been a thing all their lives.
But for people of my age, the 70s seem like only yesterday and for most of that decade Leeds were the team the Mancs obsessed over and the RS were only starting to come out of our shadow and assert themselves as the most successful team in the city of Liverpool