All these countries were involved in the fight because Austria-Hungary's demands against Serbia activated a sequence of alliances. Within weeks the major European powers were at war; their global empires meant that the conflict soon spread worldwide. At first, when the Austrian/ Hungarian prince, Archduke Ferdinand and his wife got assassinated on the 28th June, 1914. Hungary and Austria wanted independence but at the same time the other European countries wanted to rule those two countries therefore they tried to conquer Austria and Hungary. As a result there was a fight between most of the European countries.
The European countries had a lack of troops, thus they made alliances with other European countries but they all had their own demands. In this way many other countries got involved. Then the countries started making plans and tricking their partners. For example: Japan was helping Italy and Italy didn’t want to give half of the land to Japan, so Italy partnered with Greece, Serbia and Montenegro and conquered Albania.
The Italy tricked Japan by telling Greece to kill all the Japanese troops after the captured Albania. Like this the other countries made plans and distributed the small groups into allies and enemies. Allies: ENTENTIES and enemies: CENTRAL powers. The entities won the victory and Hungary and Austria got independence from each other. Another reason which could be one of the roots to the problem because the prince Archduke Franz Ferdinand was Austro-Hungarian but many Serbs lived in Austria –Hungary. So, the government predicted that this assassination was planed by the Serbs as they didn’t like the fact that they were being rules by Austria-Hungary. This was true because later it was proved that the assassin was Serbian nationalist.