The verb POLARISE comes from "pole" (like North Pole and South Pole, or like the negative or positive poles of a battery)
So the first meaning comes from physics: cause to vibrate in a definite pattern; restrict the vibrations of (a transverse wave, especially light) wholly or partially to one direction, cause (something) to acquire polarity.
Examples
"some of the light is polarized so that it vibrates in only one plane"
"polarize light waves"
"the electrode is polarized in aqueous solution".
From this comes the second meaning, which is figurative.
The second meaning is : cause to concentrate about two conflicting or contrasting positions
(as the two poles of the battery are contrasting), divide or cause to divide into two sharply contrasting groups or sets of opinions or beliefs.
Example:
"the cultural sphere has polarized into two competing ideological positions"
What you want is obviously the second meaning.
Sometimes, in election times, there are two opposing parties at opposite sides of the political spectrum, with extremely different ideas, let's call them Right and Left, and many other small parties in between. So people of the two big opposing parties try to make voters forget about the other small parties and only vote for one of those two. So people go for extremes and don't vote for moderate positions. This of course leads to communal strife and sometimes bloodshed or civil war.