As Sweden in the 1713 Siege of Tönning had lost its influence on Holstein-Gottorp, Denmark could again subjugate the entire Slesvig to the Danish realm; Holstein-Gottorps lost their lands in Schleswig, but continued as independent Dukes in their portion of Holstein. This status was cemented in the Treaty of Frederiksborg in 1720, by which the prior royal and ducal regions of Schleswig were united under the king, while the Duke remained Duke of Holstein-Gottorp under the German Emperor. The frustrated duke sought support for the recovery of Schleswig in Russia and married into the Russian imperial family in 1725. Russian Empress Elizabeth died childless in 1762, and she appointed her nephew, Duke Charles Peter Ulrich of Holstein-Gottorp, to be her successor in Russia. When he ascended the throne as Tsar Peter III of Russia, Holstein-Gottorp came to be ruled in personal union by the Emperor of Russia, creating a conflict of territorial claims between Russia and Denmark.