The Pig War
Serbia's primary export was pork which was primarily sold to Austria-Hungary. Serbia seeked to lessen their reliance on Austria-Hungary economically and thus placed a trade order with a French and Bulgarian firm. Previously, 80-90% of all Serbia's exports were related to Austria-Hungary. In turn, they reacted angrily and banned all imports of Serbian pork, ruining any trade relations they may have had in the past. Serbia retaliated by establishing trade relationships with other countries and flourishing economically.
The Bosnian Crisis
Bosnia was previously a portion of the Ottoman Empire. After the Ottoman Empire was under the threat of being broken apart by the Young Turks, they transferred Bosnia to the Austria-Hungarian Empire who were their close allies. The Bosnian Serbs living in Bosnia as well as the Serbs revolted against this annexation as they believed that Bosnia should become a part of the Greater Serbia. Russia also sided with Serbia because of their close ties but in the end Austria-Hungary threatened Russia and Serbia with war if they did not agree with the annexation. This caused Russia and Serbia to have worse relations with Austria-Hungary; ultimately contributing to the outbreak of WWI.