Answer: The main reason for other Nations being drawn into the fight was because of the alliance system which made Germany to declare their support for Austria-Hungary.
Explanation:
After the assassination of an Archduke of Austria-Hungary and his wife by Serbian nationalist, The Austria-Hungary empire declared war on Serbia. This marked the beginning of world war 1. Austria-Hungary prepared for a military invasion of Serbia after they received support from Germany, their strong ally.
Russian who was a powerful ally of Serbia, started mobilization of military against Austria, other Nations in Europe like Britain and France who are allies of Russia also declares war on Germany, as Germany had declared war on Russia. All these alliances resulted in the Nations flinging themselves into world war 1.
