You will be better searching for literature using terms such as the informal sector, informal economy, undeclared work, shadow economy, underground economy, etc. The term 'black market' has fallen out of use because of the racial connotations attached to it, namely that it is an illegitimate sphere contrasted with the legitimate 'white' economy! On the links between the 'black' and criminal economies, see the attached three papers. 

Actually a good example of black market activity is whats happens in my country: Venezuela. The origin is the use of different rate of change for the dolar. There are almost three different rates: a) at 6.30 Bs/$ for essential goods as aliments and medicines; b) around 200 Bs/$ for non essential activities as international trips; and c) around 1000 Bs/$ in the black market. The first one give place to a gigantestic source of corruption since subsidiate aliments goes, not to the population, but to a groups of persons (we named that "bachaqueros" name derived from "bachaco" which traduces the english word "ant") who transport the goods to other countries as Colombia where the products are resealing at ten times their original prices. Also, preferential dollars are given to transnational companies, as Proter&Gamble or Nestle, but the products never arrive to Venezuela, or arrive in little quantities (we call that "economic war") producing an illusory shortage of them, and when these products are offered via internet or in the street their prices are elevated to "free dollar".       

Fragile states are assumed to be those not able to pay their way. Likely a major problem in such situations is the growth of a free, but informal, market that provides necessary elements for the community. But such an informal market bypasses any tax structure–hence the danger.

The drug war in the US is an example of the wrong way to cope with an informal economy; as long as the demand exists there will arise ways of satisfying it. Co-opting it by providing the service in a controlled, safe, and less expensive manner than the informal economy is the best way.

I appreciate the views, comments and suggestions of all those who are interested in this exploration.I extend my sincere thanks and appreciation to Mr.Collin C. Williams for posting some materials to me. I warmly plead for more materials. I want to redesign my topic by critically looking at the two key concepts "black market" and "fragile state". I want the topic to now look like: Why is informal market a threat to national security., the case of Sierra Leone.

Markets, black or otherwise, are the most efficient means of providing goods to those needing or desiring them. The most efficient way of coping with a black market is not to regulate or outlaw it, but to co-opt it into the formal economy–even when it is drugs. Markets are best seen as living organisms and we all, markets and individuals, adapt to changes in our environments. That is how to cope: change the environment, and the easiest change is likely how the system is fed.

When seen as an adaptive system we can see how regulation doesn't work. Those regulated can easily adapt by gaming the system in other ways; the regulators are always playing catch-up with those gaming and the process just becomes more detailed and more expensive  with each round. Best not to go there; stick with how it's fed.