Describe the causes of the First World War

There were 4 main causes leading to the First World War. Firstly, the immediate cause of the war was the assassination of Archduke Franz Ferdinand in 1914 by the Black Hand organisation of Serbian nationalists. This led to Austria-Hungary declaring war on Serbia in revenge. Alliances also led to the war because it meant Germany had to enter the war to help Austria-Hungary and Russia joined to defend Serbia. The war became much bigger when France and Britain joined later as more and more countries had to keep their promises to defend allies. Thirdly, nationalism and rearmament led to the First World War as countries competed against each other to have larger empires and stronger militaries by building bigger battleships called dreadnoughts and designing better guns. Tensions eventually led to armies being sent to fight each other.