Complex sentence: ASL poetry emerged in the 1970s as a new art form, although ASL poetry had actually existed since the 1800s, but could not be documented or recorded because no such devices were around at that time, and also because of oppression.
Split into simpler sentences: ASL poetry emerged in the 1970s as a new art form. Although ASL poetry has truly been around since the 1800s, but couldnt be documented or recorded because no such devices were around at that time; and also because of oppression.