Early references for discrete optimization
Usually, Schrijver provides a good source for history. You can look at the following books and an article.


Alexander Schrijver. Combinatorial Optimization: Polyhedra and Efficiency. Springer 2003.
Alexander Schrijver. Theory of Linear and Integer Programming. Wiley 1998.
Alexander Schrijver. On the history of the transportation and maximum flow problems. Mathematical Programming 91(3), 2002, 437-445. http://dx.doi.org/10.1007/s101070100259 
Alexander Schrijver. On the history of combinatorial optimization (till 1960).  Handbook of Discrete Optimization, Elsevier, 2005.  http://homepages.cwi.nl/~lex/files/histco.pdf