Complex sentence: The British Government codified this, to some extent, with the publication of the Official Secrets Act in 1889 and by the time of the First World War multi-tier classification systems were used to communicate information to and from various fronts.
Split into simpler sentences: The British Government codified this, to some extent, with the publication of the Official Secrets Act in 1889. By the time of the First World War multi-tier classification systems were used to communicate information to and from various fronts.