• The start of World War One is not simple. It involved a combination of events.

At the beginning of the 20th century, Serbia was part of the Austria-Hungary empire. Around 1904, Serbia wanted to expand so it decided to break free of it's economic dependence on Austria-Hungary by trading with other countries. At this time, Serbia's major export item was pork and Austria-Hungary was their biggest customer. To punish Serbia, Austria-Hungary created an "economic war" by stopping the import of Serbian pork in 1906. This backfired because Serbia was able to find other customers and increase it's exports. As a result, relations between Austria-Hungary and Serbia began to sour.

• Then in 1908, after a change in foreign ministers, Austria-Hungary tried to annex some Balkan (Serbian) territory. This angered Serbia even more.

Then between 1912 and 1913, Serbia was involved in two Balkan Wars. The first Balkan War involved Serbia, Greece, Bulgaria and Montenegro fighting against the Turks of the Ottoman Empire. The Turks were defeated in the first Balkan War. But Serbia, Greece, Bulgaria and Montenegro could not agree on who gets what land they had captured. So the Bulgarians attacked the Serbians and the Greeks. Then the Romanians and Turks attacked the Bulgarians. By the time both Balkan wars had ended, Serbia had added lots of captured territory to it's empire and this made Austria-Hungary even more concerned.