Complex sentence: He maintained close relationships with both Khalka Mongol leaders and the spiritually devout Kangxi Emperor and when efforts to unite Khalkha and western-based Oirat-Dzungar Mongol tribes failed, Zanabazar played a key role in negotiating the Khalkha Mongol submission to Qing rule in 1691.
Split into simpler sentences: He maintained close relationships with both Khalka Mongol leaders and the spiritually devout Kangxi Emperor. When efforts to unite Khalkha and western-based Oirat-Dzungar Mongol tribes failed, Zanabazar played a key role in negotiating the Khalkha Mongol submission to Qing rule in 1691.