As it turns out, there is an answer to that question. Athens. And Athens got it from Cleisthenes, who set up some critical reforms. For those engaged in nation building, you might want to take a look at how he did it. Check out Tom Holland's Persian Fire, where the difference between Darius's Persia and Athens are clearly laid out. Cleisthenes set out some key reforms:
1. Equality before the law (isonomy) was the chief political virtue, and representatives of each of the demes were selected by lot for service.
2. All citizens enjoyed freedom of speech.
3. Government policy requires open debate in the assembly.
4. New laws may not be passed except by vote.
5. Families were to be destroyed as the basis for political association: membership in a deme was the basis of being selected.
Let's look at that last. Athens had problems with families which feuded with each other. Cleisthenes key insight was that Attica was separated into these families, and the influential ones had too many members in too many places. So he created 150 districts to elect members of the assembly, and required EVERYONE in each district to take the district name as their last name, effectively cutting off the connection between political representation and clan membership. This reform is the one that is desperately needed in places like Iraq, where family and tribe are primary influences.
Hat tip to Roger Sandall for an illuminating article, whose site Culture Cult has amply repaid the time to read it, and whose thought has greatly influenced me (and who has thought about Tom Stoppard in a way that allowed me to appreciate Stoppard again).