The cause of the First World War was that Serbian national activists used a few bear children to kill the Austro-Hungarian prince (the killers were Bosnians, but Serbia considered itself the homeland of all Serbs in the Balkans, and the black hand that organized the assassination was formed by members of the Serbian military and political departments, and there were seven killers that day), but after the incident, the most active were Tsarist Russia and Britain and France, who supported Serbia and caused the outbreak of World War I.
The reason why Tsarist Russia supported Serbia was simple: Great Slavism, the tsar was to be the savior of all Slavs, and Nicholas II preferred to sacrifice his own savings for the sake of the Yugoslavs. The Romanov family from Tsar Nicholas II was not rich in military geniuses (Peter the Great's military talent did not reach the genius level, and the Swedish Vasa family and the Prussian old Huo family were not comparable), and this family was able to take power in Russia to play the role of the savior of the Slavs. At the end of the 19th century, the Crimean Khanate had long since fallen, the Ottoman Empire was also beaten by Tsarist Russia as the sick man of West Asia, and the place where Tsar Nicholas II showed his feelings became the Balkan Peninsula. Nicholas II supported the Slavic Society, the Moscow Slavic Charity Committee and other organizations that frequently expanded their influence in the Balkans, and also brought many Serbian refugees to Tsarist Russia at his own expense (he turned a blind eye to the suffering of the Tsarist population itself).
Before the outbreak of the First World War, Nicholas II had even more deposits in Germany than in his own country, depositing 12 million gold rubles in his country's banking system, but 15 million gold rubles in German banks that were about to fight him. For the liberation of the Serbs, the tsar was willing to have this deposit worth 370,000 taels of gold confiscated by the Germans.
Tsarist Russia wanted to maintain its own character, and did not hesitate to lose money and support Austria-Hungary Germany to go to war. Britain and France simply felt sorry for their own investments, so they stood with Tsarist Russia. After the end of World War I, Britain, France and other countries calculated their investments and found that they had bought Russian bonds worth 18.5 billion gold rubles. This money is converted into 448 million taels of gold, which is 20.6 billion silver.
Most of this money was owed by Nikolai during his reign, and during the Russo-Japanese War, he owed France a debt of six billion francs. France not only bought most of the Tsarist Russian bonds, but also made huge investments in the country. Since France's coal reserves are only a little more than 700 million tons, and it is impossible to carry out a large-scale integrated coal and iron industry in its own country, after the discovery and mining of the Donbas coal mines with hundreds of billions of tons of stock in Tsarist Russia, the entire investment circle in Paris was excited about the New Year, and French capital quickly won two-thirds of the share of coal and steel investment in Tsarist Russia.
French capital also burned 2.4 billion francs in the arms industry of the Tsarist army, and the famous French arsenal Schneider Company also manufactured artillery in Tsarist Russia, and the military industry of the two countries has a close relationship, so much so that a large part of the famous Russian rifle Mosin Nagant is made by the French. Schneider & Co. also propped up a lesser-known politician, Raymond Poincaré, who accidentally became president before World War I. France's financial, industrial, and military industries are all tied up with Tsarist Russia, and naturally advance and retreat with Tsarist Russia, implementing the contract that has already been signed, according to which Tsarist Russia was violently beaten by Germany, and France will send 1.3 million troops (France sent troops in World War I is 5 times the share)
The British also had huge investments in Tsarist Russia, and in addition to finance, the oil industry in Tsarist Russia was monopolized by British and Swedish capital (that is, the Nobel family). In the face of huge interests and conflicts, it really doesn't matter who is the sufferer.