Perhaps the most ominous common pattern has been a backlash by others who resent the special preferences given to particular groups. In India, violence against Dalits has escalated in the wake of preferences on their behalf -- preferences which, ironically, relatively few Dalits are able to take advantage of.
In Sri Lanka, where the groups live concentrated in different regions, the escalation of violence has gone all the way to civil war. This small nation has suffered more deaths from this internal strife than the United States suffered during all the long years of the Vietnam war.
Where have large-scale group preferences been successful, at least in the sense that they have benefitted large numbers of people in one group without either ruining another group or degenerating into violent internal strife? Malaysia may be the prime example, but it has had unique features that may not enable it to be a model for other countries.
First, group preferences in Malaysia began in 1970 and were carried out while the country experienced unusually rapid economic growth and transformation from a predominantly agricultural nation to a modern commercial and industrial society. A rising tide raised all boats.
Another key factor is that it is a federal crime in Malaysia to promote intergroup strife. There can be no careers like those of Jesse Jackson or Al Sharpton in Malaysia. For countries where free speech is basic, Malaysia is not a model that can be imitated.