How did the family feud amongst Queen Victoria's descendants provide a catalyst to WWI?

Queen Victoria's descendants were the rulers of many nations that were involved with each other in the war.

Explanation:

The rulers of most of the empires of the time had some relation to Queen Victoria by marriage alliance.

This meant that the war was ultimately broken out between relatives who fought against each other, which is of course, common in the time of monarchies as most monarchies were related to one another through marriage.

Queen Victoria's relatives included the royal family of the Austria Hungary empire, The German king and the Tsar Nicholas II of Russia, and of course the royal family of England.