It can be subtle, but generally if the "others" are identified with attributes like "inferior", "threat", "danger", etc., the society is on track for massacre or war. The stronger this division is, the closer the society is to some atrocity or another.
If the side that's "othering" a group has great or vastly imbalanced power, then the result is likely to be a massacre. If not, then it's likely a war will occur.
It's sometimes hard to tell if a group is being "othered", but generally if you can replace a generalization with the word "others" or "those people" and it sounds sinister, then that's probably what's happening.
Examples:
"The Patriots defeated the Giants."
Rephrased: "The Patriots defeated the others."
Not sinister; no threat of massacre/war.
"The Russians attacked our voting infrastructure in 2016."
Rephrased: "The others attacked our voting infrastructure in 2016."
Somewhat sinister; possibly war.
"Muslims have attacked two buildings in New York.".
Rephrased: "Those people have attacked two buildings in New York."
Sinister; risk of massacre.
"Whites are responsible for implicit racism by nature of their history of oppression."
Rephrased: "The others are responsible for implicit racism..."
Somewhat sinister; possible war or massacre.
"Adults are increasingly falling into debt."
Rephrased: "Those people are increasingly falling into debt."
Not sinister.
"Blacks are responsible for 5x more murders than whites."
Rephrased: "Those people are responsible for 5x more murders than us."
Sinister; possible massacre.
The frequency and intensity with which you witness these types of phrases—especially in the face of increasing generalization that captures less and less aspects of individuality—the closer you are to something bad happening.
And if it's accepted as de facto with no room for nuance or argument, then your society is likely on the precipice of atrocity.
The best way to fight it? Recognize when it happens and call it out for what it is: dehumanization.