Complex sentence: She wanted to persuade Henry II of France to withdraw his troops from three fortresses that the Ottomans had captured in Banat, so she sent Christopher to France to start negotiations in 1557.
Split into simpler sentences: She wanted to persuade Henry II of France to withdraw his troops from three fortresses that the Ottomans had captured in Banat. For this purpose, she sent Christopher to France to start negotiations in 1557.