I assume that you are talking about the Balkan Wars of the early 1910s and the assassination of Archduke Franz Ferdinand.  If so, the Balkan War led to the assassination because they inflamed Slavic nationalism and hatred of Austria-Hungary.

The Balkan Wars mattered because Serbia was using these wars to take more territory, in particular a port on the Adriatic Sea (access to the ocean is very important for economic and military reasons).  Austria did not want Serbia to get these territories.  After the wars, Austria (with help from other European nations) forced Serbia to give up the territories it had gained.  These actions made Serbia (and the Slavs in the region who identified with Serbia because it was a Slavic country) very angry at Austria.  This anger led to the killing of the Austrian Archduke.

What was the assassination of Archduke Franz Ferdinand?

The assassination of Archduke Franz Ferdinand of Austria-Hungary was the spark that is credited with setting off World War I.

The Archduke was the heir to the throne of Austria-Hungary.  This was a multiethnic empire whose rulers were ethnically German.  Many of the people that they ruled were Slavs.  This was the case in the Balkans, in places that later became Yugoslavia and have now broken up into countries such as Serbia, Croatia, and Bosnia.  The Slavs did not like being ruled by people who were ethnically different from them.  Therefore, there was a Slavic nationalist movement in that part of the empire.  It was supported by Serbia, then an independent country, and Russia, both of which were Slavic countries.

On June 28, 1914, the Archduke was visiting Sarajevo, in what is now Bosnia.  There, he was assassinated by a Slavic nationalist.  In response, Austria-Hungary, which was looking for a reason to go to war with Serbia anyway, issued an unreasonable ultimatum to that country.  When Serbia would not accept all the terms of the ultimatum, Austria-Hungary went to war.  This triggered the more general war that we now know as WWI.