I think that it is  the existence of one or more inequalities at the same time that leads to conflict and the more severe the inequalities the more severe or persistent is the conflict.  However, I notice that the model you mentioned above of Frances Stewart appear to leave out the role of environmental inequality.  When marginalized groups are left out or pushed out of a development process unsustainability should be expected.  I tried to make the point in one of my papers that we should expect an increase in the risk of social unrest when the supply of agricultural commodities of high social value decreases as a result of policies promoting the increase production of goods of low social value, and this it is said leads  to an expected cycle of social unrest.  When you have time you can read the ideas supporting this point:

Agriculture and Global Warming: Should the Biofuel Route Be Expected to Be a Socially Friendly Agricultural Policy?

https://www.researchgate.net/publication/281276235_Agriculture_and_Global_Warming_Should_the_Biofuel_Route_Be_Expected_to_Be_a_Socially_Friendly_Agricultural_Policy

Have a nice day

Lucio

Article Agriculture and Global Warming: Should the Biofuel Route Be ...

Dear Bikash,

The last conflicts in ex-Yugoslavia, Middle East (Syria, Afghanistan, Iraq...), Latin America (Colombia, El Salvador, Guatemala...), Africa (Sudan, Congo, Etiopia...) are the results of war for land. The land have the power and the richness. And the access to the land, offer the possibility of equality.

The inequality is produced due the concentration and monopolization of land in the hands of very few persons.

And the war around the world, born in the same situation: the violent land grab.

Thanks Lucio and Luis for your valuable insights , much appreciated. I fully agree with the role of the inequality in  environmental and agricultural land dimension as  much ( or even more ) importance as other dimensions in fueling group violent conflict in multi-ethnic societies. Yet my pertinent question is about any threshold evidence thus far of  what degree of such inequalities ( as measured by Gini coefficient or other measures) can catalyze civil conflict because of the persistence of some degree of such inequalities  in every developing countries.    Thanks again for your valuable answer.   

Conflict is not simply a product of a "land grab."  To better understand the sources of conflict, you are better served examining the concepts of relative depravation and opportunity cost of conflict.  Institutional instability, resource scarcity, food insecurity, etc., all alter the opportunity cost of conflict.

To your point, there is very little evidence of thresholds because it is a multi-dimensional problem.  And, it is not just an economic problem.  There are social, political, and economic dimensions interacting, and "inequality" is not particularly pertinent.  That is, it is "relative inequality" that matters.  And that is only operational in the context of weak institutions that prevent Coasian bargaining in the first place.  

Many thanks darren for  clarifying very little evidence of threshold given its  complex interacting  multidimensional nature of relative inequality that deserve further research using such holistic perspective.   

Following up on Luis Fernando comment, you may find my publication related to land reforms at the heart of conflicts interesting focusing on the sustainability requirements, whic are usually missing,

The Search for Equity in Access to Land in Latin America: Which Are the Main Characteristics that Define a Sustainable Land Reform Model?

https://www.researchgate.net/publication/282199695_The_Search_for_Equity_in_Access_to_Land_in_Latin_America_Which_Are_the_Main_Characteristics_that_Define_a_Sustainable_Land_Reform_Model

Article The Search for Equity in Access to Land in Latin America: Wh...

Thanks Lucio for providing your interesting paper.