Nationalism
Nationalism was an extremely strong force in the 19th and early 20th centuries. Nationalism is best understood as a force that unites people because of perceived similarities, such as a common language, ethnicity, religion or culture. People who are nationalistic want their country to be strong and powerful, and they believe that their way of life is superior to others. Nationalism helped cause war in two ways.
First, it made the people of countries like Britain, Germany and France more warlike. French politicians (like Clemenceau and Poincare, who had been around in 1870 during Bismarck's Franco-Prussian War) despised the Germans and stirred up nationalistic fervour to get elected.
Second, it made the different ethnic groups ruled by the Ottoman Empire (such as the Romanians and the Bulgarians) and by Austria-Hungary (such as the Serbs) want to be free. In the Balkans, this was called Pan-Slavism because the people who wanted to be free were all of Slav ethnicity. The most nationalistic of all were the Serbs. Serbia had become an independent country in 1878, but in 1900, many Serbs were still ruled by Turkey and Austria-Hungary. The Serbian government was determined to rule over them all.
First, it made the people of countries like Britain, Germany and France more warlike. French politicians (like Clemenceau and Poincare, who had been around in 1870 during Bismarck's Franco-Prussian War) despised the Germans and stirred up nationalistic fervour to get elected.
Second, it made the different ethnic groups ruled by the Ottoman Empire (such as the Romanians and the Bulgarians) and by Austria-Hungary (such as the Serbs) want to be free. In the Balkans, this was called Pan-Slavism because the people who wanted to be free were all of Slav ethnicity. The most nationalistic of all were the Serbs. Serbia had become an independent country in 1878, but in 1900, many Serbs were still ruled by Turkey and Austria-Hungary. The Serbian government was determined to rule over them all.