Question

Question #5fbb6

Answer 1

It was directly triggered by the assassination of the Austrian archduke, Franz Ferdinand and his wife, on 28th June 1914

Explanation:

This is just a simple answer but there is more. One of the reasons many countries got involved was due to alliances between countries that occurred before the war.

These were important because they meant that some countries had no option but to declare war if one of their allies, declared war.