In 1207, the Mongol ruler Genghis Khan (r. 12061227) conquered and subjugated the ethnic Tangut state of the Western Xia (10381227). In the same year, he established diplomatic relations with Tibet by sending envoys there. The conquest of the Western Xia alarmed Tibetan rulers, who decided to pay tribute to the Mongols. However, when they ceased to pay tribute after Genghis Khan's death, his successor Ogedei Khan (r. 12291241) launched an invasion into Tibet.
Which ruler took Western Xia under their control? (If the question is unanswerable, say "unanswerable")
Genghis Khan