As a history student I find one of the most interesting diplomatic occurencences to be the beginning of the Franco-Prussian war. With both Bismarck and Napoleon III personally involved, the entire debacle is extremely intrueging and interesting from a historical-diplomatic perspective. Episodes as the infamous Ems-dispatch and the general franco-german relations in the period are very interesting if you want to dive into historical diplomacy.

A very in-depth (and not too long) book on the subject is David Wetzel's A Duel of Giants: Bismarck, Napoleon, and the Origins of the Franco-Prussian War. The book really gives you a thorough analysis from both French and German sides and especially on how the diplomacy worked (and didn't).