But for the vast majority of history people did not live in inclusive democracies, and many governments were able to provide stability (for a time) despite this fact. Our notions of democracy today are also directly being challenged by China which supposes it can maintain stability and popular support from the vast majority of its citizens without even allowing them a voice in government at all. So far, despite its methods, it seems to be doing well enough. There's also plenty internal turmoil in the supposedly well functioning 21st century inclusive democracies for all sorts of reasons.
There's a certain degree of power asymmetry between groups which if imposed/maintained could and likely will lead to conflict, but that is true in any form of government and I don't think it's a sure bet that democracy/more democracy is the best way to guarantee access that feels equal enough for all groups. Democracy doesn't work all that well at scale either. The larger the population, the harder it will be to make everyone feel like they have a stake and representation in government.