The house became "boyars" (the highest rank in Russian nobility")" of the Grand Duchy of Moscow and later of the Tsardom of Russia under the reigning Rurik dynasty, which became extinct upon the death of Tsar Feodor I in 1598. The Time of Troubles, caused by the resulting succession crisis, saw several pretenders and imposters (False Dmitris) fight for the crown during the Polish–Muscovite War of 1605-1618. On 21 February 1613, a Zemsky Sobor elected Michael Romanov as Tsar of Russia, establishing the Romanovs as Russia's second reigning dynasty. Michael's grandson Peter I, who established the Russian Empire in 1721, transformed the country into a great power through a series of wars and reforms. The direct male line of the Romanovs ended when Empress Elizabeth of Russia died in 1762, thus the House of Holstein-Gottorp (a cadet branch of the German House of Oldenburg that reigned in Denmark) ascended to the throne in the person of Peter III. Officially known as members of the House of Romanov, descendants after Elizabeth are sometimes referred to as "Holstein-Gottorp-Romanov". The abdication of Emperor Nicholas II on as a result of the February Revolution ended 304 years of Romanov rule and led to the establishing of the Russian Republic under the Russian Provisional Government in the lead-up to the Russian Civil War of 1917-1922. In 1918 Bolshevik officials executed the ex-Emperor and his family. Of the House of Romanov's 65 members, 47 survivors went into exile abroad.