World war I

In 1914, the Crown Prince and Princess of Austria-Hungary were shot and killed in the Kingdom of Serbia by Serbian nationalist Gaurilo Princip. =Putting pressure on the Hungarian Empire, Emperor Franz Joseph I of Austria-Hungary sent an ultimatum to the Kingdom of Serbia in response to the incident. Declare war on Serbia, followed by Germany declaring war on Serbia on the side of Austria-Hungary, Russian empire starting all-out mobilization to protect Serbia, and German empire stopping all-out mobilization against Russian empire. The Russian Empire refused the German Empire's demands, and the Russian Empire declared war on the German Empire on the side of the Kingdom of Serbia. World War I began, and as the war progressed, the Kingdom of Bulgaria, which had a grudge against the Kingdom of Serbia after being defeated in the Second Balkan War, declared war on the Kingdom of Serbia on the side of the Austro-Hungarian Empire, and the Ottoman Empire also won the war. Austria-Hungary entered the war on the side of Austria-Hungary and declared war on Serbia, Italy between Austria-Hungary and Germany. Although there was an alliance, Serbia entered the war on the side of Serbia in order to obtain territory from the Austro-Hungarian Empire and declared war on the German Empire. entered the war on the side of the Kingdom of Serbia and declared war on Germany. and became a war between the entente camps of the Russian Empire and the Kingdom of Italy.