One half century earlier, the englishman charles darwin introduced his idea of evolution, which was based on the idea of survival of the fittest. do you think von bülow believed in this idea?

Assuming you're referring to Bernhard von Bülow, yes it is likely that he approved of this idea, since he was a leading diplomat in Germany during Germany's colonial period, which was largely justified as "stronger" nations preying on "weaker" ones, especially in Africa. 

Southern secession is the event or issue that historians can gain insight from this excerpt.