This is a very simple, and yet, highly complicated subject.
It's possible, but yet, it's a highly difficult task.
It's simple, because the root cause of unrest and disharmony in the world is ignorance and egoism. If the minds are free from ignorance and egoism, there will be minimum unrest and disharmony but more peace and harmony in the world of diversity. And, it's possible for the minds to be free from ignorance and egoism.
It's highly complicated as well as extremely difficult, because most minds are deep rooted in ignorance and egoism, and it has to come from the minds themselves to be aware of ignorance and egoism, and be initiated to free themselves from ignorance and egoism, particularly those who have the influencing power and authorization towards decisions making in the world of authorities or leaderships, as well as those who are bringing up and educating the younger generations who are the future members of the society/influencers/educators/leaders that are influencing and determining everyone's thinking, behavior, actions and reactions, that are impacting the condition and situation and everyone's existence and life in the world that doesn't belong to anyone at all.
And hence, it's not that easy to promote peace and harmony in the world of diversity, unless majority of the minds, including those who think they are highly educated, intelligent, knowledgeable, successful, ambitious and influential, especially those who have the opportunity and influencing power to be impacting the general condition and situation of the world in certain way, start to be aware of the ignorance and egoism in themselves, where most minds are naturally being over-powered by survival instinct, on top of the stubborn egoism of attachment, identification, desire of craving and aversion, judgment and expectation, that give rise to many elements that feed and empower unrest and disharmony in the world of diversity, such as possessiveness, ownership, invasion, occupation, sense of belonging, grouping, politics, patriotism, nationalism, pride, heroism, self-righteousness, selfishness, greed, hoarding, fear, protectiveness, defensiveness, closed-mindedness, corruption, stinginess, exploitation, desperation, discrimination, separateness, prejudice, hatred, control, interference, oppression, outcast, offensiveness, violence and war.
All these products of ignorance and egoism exist in most minds, including the minds that think and believe that they are good, righteous and generous human beings who love goodness, prosperity, love, peace and harmony for 'all', but only within their own group that they identified as 'them' or 'theirs', that they 'love', 'protect', 'agree with' and 'share with', a community that is based on their particular common background, names and forms, belief, values, practice, vision and desire, where they think and believe that they need to protect 'themselves' and 'theirs' from 'the others' that are not 'them' or 'one of them', that they feel intimidated, dislike, disagree with and don't want to share with.
The wise, compassionate, desireless, intentionless and selfless minds, of the many enlightened buddhas and gurus, also cannot remove the ignorance and egoism as well as the consequences of ignorance and egoism in the world. They only disseminate the teachings and practice of how to free one's mind from ignorance and egoism into the world, and let everyone whether to be aware of the ignorance and egoism in themselves, and be initiated to be free from ignorance and egoism through their own self-effort, self-discipline, self-inquiry and self-realization.
The many minds that have good intention and aspiration of hoping to change the world to be a better place, not that there's anything wrong or bad with such intention and aspiration, however, it indicates that they are also under the influence of ignorance and egoism, or else, there won't be any intention or aspiration of hoping to 'change' the world, as that idea/desire/intention/aspiration is also part of the egoism deriving from ignorance, that is the reason why the world is what it is now, which is and will be more and more unrest and disharmony.
The protective self-righteous minds under passionate egoistic attachment
and personal/group identification towards certain qualities of names
and forms will react with anger, hatred, resentment and violence towards
something that they perceived as 'bad', 'wrong', 'humiliation',
'disrespectfulness', 'belittling', 'offensiveness', 'hurtful',
'undeserving', 'going against their desire', or 'disagreeable in
accordance to their thinking, belief, values and practice'. The selfless
minds are aware of the many unpleasant and disagreeable
actions/reactions and their consequences in the world of countless minds
ceaselessly acting/reacting under the influence of ignorance and
egoism, but without being disturbed or determined by all these ignorant
egoistic behavior, affair, condition and situation. Reaction of anger,
hatred, resentment and violence will not help to promote peace and
harmony in oneself and/or the world, but only contributing more unrest
and disharmony in oneself and into the world.
Unless, all minds start to let go of the idea/desire/intention/aspiration of "We want our world to be and not to be in certain way." Then the world will be what it is, in peace and harmony, having all kind of diversities, of many different colours, names, forms and shapes, sharing the space without possessiveness, when nobody desire the world to be only in certain colour(s) that they personally like and prefer, 'interfering'/'influencing'/'changing'/'making'/'controlling' the world to be in certain way that they like and desire and not to be in certain way that they don't like and don't desire, but allowing the world to be what it is.
The world will be what it is, in peace and harmony, when nobody try to spread 'self-righteousness', 'fear', 'possessiveness', 'protectiveness', 'separateness', 'discrimination' and 'hatred' into the world in order to harvest power by over-powering the others, in order to achieve their particular desire/aspiration/vision of making the world that doesn't belong to anyone to become 'their world the way that they desire'.
The world is so 'quiet' and peaceful, as it is, free from unnecessary egoistic actions and reactions, unrest, chaos, conflict, discrimination, prejudice, lies, manipulation, plotting, scheming, scamming, slandering, politics, corruption, greed, desire, ambition, invasion, interference, fear, separateness, jealousy, hurt, hatred and violence generated by passionate ambitious minds under the influence of ignorance and egoism, when all minds are either absent/have gone to sleep/resting in silence/void of ignorance and egoism.
Inquire the truth of everything.