The Brusilov Offensive ( "Brusilovskiĭ proryv", literally: "Brusilov's breakthrough"), also known as the "June Advance", of June to September 1916 was the Russian Empire's greatest feat of arms during World War I, and among the most lethal offensives in world history. The historian Graydon Tunstall called the Brusilov Offensive the worst crisis of World War I for Austria-Hungary and the Triple Entente's greatest victory, but it came at a tremendous loss of life. The heavy casualties eliminated the offensive power of the Imperial Russian Army and contributed to Russia's collapse the next year.