I agree that the rise of nationalism was the most important factor leading to World War I as it increased tensions among Serbia and Austria-Hungary resulting in the direct cause of World War I. The Balkan crisis’s in 1908 and 1912-13 involving the annexing of Bosnia and Herzegovina by Austria-Hungary. Serbia wanted to expand into the Adriatic Sea as a result of the second Balkan crisis but was denied by Austria-Hungary. Serbia was supported by Russia who however was forced to back down by Germany. Also, as a result of the annexing and rising political tensions between both countries, a Serbian nationalist, Gavrilo Princip assassinated the heir to the Austrian-Hungarian throne Archduke Franz Ferdinand and his wife Sophia, Duchess of Hohenberg. This shows that Nationalism was the cause as it spread through Serbia as Bosnia and Herzegovina contained around 3 million Serbians, but was refused control over the country by Austria-Hungary. Also, Serbia was denied expansion into the Adriatic Sea, which greatly increased the discontent of Serbian nationalists towards Austria-Hungary culminating in the assassination. The assassination led to World War I as the search for the organisation backing the assassin was denied by Serbia, leading Austria-Hungary to declare war on Serbia on July 28 1914. Therefore nationalism was the most important factor leading to World War I as it increased tensions between Austria-Hungary which resulted in the direct cause of World War I.
However I disagree with the statement as Imperialism was also an important factor to World War I as Imperialist rivalry between the European countries increased tension amongst them. In the late 1800s, more developed European countries set out colonising the more underdeveloped territories in Asia and Africa. 10% of Africa was colonised in 1880, compared to 90% in