Answer:
alot the most one that lead to world war one was the assasination of archduke franz ferdinand was killed as they wanted revenge.
they wanted to capture and execute princip but serbia did not allow it as they went into war as they do not get along.
the luisiania sunk and the germans were the one who did from submarines which makes america and british mad.
nationalism each country wanted to prove that they were powerful and had the right to conquer the world.
and basically because the one helped another and it would create more problems and relationships with other countries.
~batmans wife dun dun dun....