Sentence:  Among the many severe measures taken by the First Emperor , Shih Huang-ti , in his efforts to <WSD>insure</WSD> the continuation of this hard-won national unity , was the burning of the books in 213 B. C. , with the expressed intention of removing possible sources for divergent thinking ; but , as he had a special fondness for magic and divination , he ordered that books on these subjects should be spared . 
Meaning of the word marked with <WSD> tags:  be careful or certain to do something; make certain of something