Oh boy... I think you will find the answer in George Orwell's Animal Farm.
But to help you understand, rewriting the past to sustain power is the type of thing that degenerates into genocide for example.
In the short term it might look innocuous, but if corrupting truth and suspend basic moral and ethic values on something as basic as History, what other basic human values are you willing to suspend because you don't like how something feels?
This is the breeding ground for racial supremacists, ethnophobia, etc. Terrible stuff.
And you don't need to go into the past to see the consequences, Ukraine is fighting for their existence because a group of people in Russia don't want to acknowledge that a ethnic group they deem inferior can have better chances at thriving than them, to the point of denying Ukrainians existence all together.
