Which change made by the cherokee most them preserve their history?

The Cherokee developed a syllabarie (like an alphabet but instead of letters, it is composed of syllables), and that allowed them to get literate.

This syllabarie was developed by Sequoyah in 1809. Sequoyah was a cherokee was silversmith, and while he spoke no english, he had so much contact with white customers that he realized the importance of writing and worked years in the development of a writing system for his people.

Years later, the syllabarie had had so much success that the Cherokee had a higher literacy rate than the white farmers who lived nearby.