I have a Shorter OED, 1993 edition. It tells me that the word originated M20, that is mid-20th C. A little further digging tells me racism and racist showed up around 1930 and were common in English by the late 30s. There were earlier versions of racialism and racialist from 40-50 years earlier. The SOED at the time carried the theory that all members of each race possess characteristics, abilities, qualities, etc specific to that race, esp distinguishing it as inferior or superior to another race or races; prejudice, discrimination, or antagonism based on this.
A more modern definition from Merriam-Webster is a touch different: a belief that race is a fundamental determinant of human traits and capacities and that racial differences produce an inherent superiority of a particular race
All of the early entries treat this as absolutist. All members...specific to that race...inferior or superior. There is nothing of tendencies, nor anything of mere differences with no ranking. The later definition softens that some, that one's race is a "fundamental determinant." Still, that's pretty strong.
But the Merriam-Webster also includes something new, a second definition that refers to systemic oppression, or a system founded on racism. I am not concerned whether we think this definition is wrong or what we think it should mean, because dictionaries have not been prescriptive like that since the 1960s. Dictionaries record how words are actually used, without judgement. I simply note that this second definition is new. There is a hint of it in the portion of the 1993 definition after the semicolon. I don't know how new. As this is a shading of one meaning into another, the emergence might be hard to pin down. It may have already been used in that way in 1993, just not frequently. My impression is that this second meaning is about ten years old, twenty at most. Part of postmodernist jargon is redefining words and then applying social pressure to make sure you are keeping up. Fashion and fad are features, not bugs. Language is a very important weapon to leftists* including insisting that their definition is the only real one. This is all just tactic, with no intellectual foundation.
For comparison, the words sexism and sexist came in in the 1960s and in the Shorter Oxford in 1993 had definitions similar to the one for racism. M-W has not added in a second definition for sexist of oppressive systems on it's current site. I don't doubt someone has used sexist in that way, but it has not yet become common enough to be generally accepted as common.
Words change in meaning. Taking on an additional meaning or dropping an old one is very common historically, and I recognise that my irritation at that level is largely from just being an old guy. But language change when initiated from the left is quite different. It is not something which flows naturally, but is calculated. So too here. The new definition is not merely an addition, it is an attempt to draw from the extreme negative emotional energy attached to the first definition of racism so as to apply it to the second. They want to call you racist on the basis of the second definition but get all the juice of thousands of years of real racism thrown in in order to get votes, grant money, jobs, status...hell, in order to get power, because for leftists there is nothing but power. Any intellectual argument you have against them is just an excuse for maintaining power.
It is a word game, and it isn't anything else.
A close analogy would be the express tactic communists used, including in America, of rewriting the lyrics to religious music to suit political ends. In the US, that was old hymns. "Down by the Riverside," "Michael, Row the Boat Ashore," and most famously, an entirely spiritual meaning being entirely swamped in the political. I once sang this song with fervor as a 16 year-old. Now I cannot listen to 30 seconds of it.
Deceptive bastards, right out of the gate, trading on the emotional associations that other people paid in blood to earn, but they stole.
*I don't mention enough that the distinction between liberals and leftists is growing ever more profound philosophically. I have anger at liberals because they do not see that, and believe that those really dangerous people must be just like them, because they hate Trump and racism. Yet the people in power in government and academia and entertainment are increasingly different from those nice folks who go to discussions at the library or shudder at those Creationists they just don't understand, mind-read that those conservatives must be speaking in code and are mostly Nazis, and have always been deeply concerned about
acid rain, the tropical rainforest, global warming, climate change. I get angry at them, but I don't think they are crazy or even that their values are askew. Their values are mostly fine - but entirely irrelevant in the current political climate.