This is an absolute statement as division is literally caused by dividing between "sides". You get a divided country when the people within it divides each other into sides. Its never been the case when people have said "our side has caused the division". never.
That is the irony you should be finding! If you do finally see this irony you might find more nuance, but maybe more frustration and more uncertainty and confusion but less anger and possibly more empathy to the other. That's why its so easy for people to divide, as its less painful. Dividing and categorizing is how we make sense of the world, but it can be a curse too.