Complex sentence: In 1742, Empress Elizabeth of Russia brought Anna's son, her nephew Peter of Holstein-Gottorp, to St. Petersburg and proclaimed him as her heir and would, in time, marry him off to the German princess Sophia of Anhalt-Zerbst.
Split into simpler sentences: In 1742, Empress Elizabeth of Russia brought Anna's son, her nephew Peter of Holstein-Gottorp, to St. Petersburg and proclaimed him her heir. In time, she married him off to the German princess, Sophia of Anhalt-Zerbst.