The "elaborate alliance systems" among European powers, "each secured by a network of secret treaties, financial arrangements, and 'military understandings'" are commonly cited as one of the causes of World War I.[4] For example, the Reinsurance Treaty of June 1887 between the German Empire and the Russian Empire (negotiated by German Chancellor Otto von Bismarck in order for Germany to avoid a two-front war), was a "highly secret treaty" in which the two powers pledged a three-year period to remain neutral should the other become involved in a war with a third country, unless Germany attacked Russia's longstanding ally France or Russia attacked Germany's longstanding ally Austria-Hungary.[5]