Complex sentence: The historical consensus is that responsibility or guilt for the war was not attached to the article, but that the clause was a prerequisite to allow a legal basis to be laid out for the reparation payments that were to be made.
Split into simpler sentences: The historical consensus is that responsibility or guilt for the war was not attached to the article. Rather, the clause was a prerequisite to allow a legal basis to be laid out for the reparation payments that were to be made.