Complex sentence: When Sitchin wrote his books only specialists could read the Sumerian language, but sources such as the 2006 book "Sumerian Lexicon" have made the language more accessible to non-experts.
Split into simpler sentences: When Sitchin wrote his books, only specialists could read the Sumerian language. However, sources such as the 2006 book "Sumerian Lexicon" have made the language more accessible to non-experts.