Complex sentence: White provides a system to de-mystify histories, historians, journalism, and journalists who claim to present things objectively, while providing some methods for determining in what ways a given account lacks "complete objectivity" and how it can be seen as ultimately ideological.
Split into simpler sentences: White provides a system intended to de-mystify histories, historians, news reports, and journalists who claim to present things objectively. He also proposes some methods for determining in what ways a given account lacks complete objectivity and how it can be seen as ultimately ideological.