To be sure, the notion of ethnicity in pre-colonial Burma was highly fluid, heavily influenced by language, culture, class, locale, and indeed political power. People changed their in-group identification, depending on the social context. The success and longevity of the Pagan Empire sustained the spread of Burman ethnicity and culture in Upper Burma in a process that came to be called "Burmanization", which Lieberman describes as "assimilation by bi-lingual peoples, eager to identify with the imperial elite". According to Lieberman, Pagan's imperial power enabled the "construction of Burman cultural hegemony", evidenced by "the growth of Burmese writing, the concomitant decline in Pyu (and perhaps Mon) culture, new trends in art and architecture, and the expansion of Burmese-speaking cultivators into new lands".