Warhammer 40,000 – My heyday for 40K was in the early 2000's. At that time it seemed like the hobby was huge in my area with worldwide campaigns, weekly tournaments, convention support you name it. It was a glorious time to be playing Warhammer 40K.
During that time period Black Library was really just coming into it's own and was publishing art books and background books. Among these were the Battle for Armageddon and the 13th Black Crusade. Each of these books took the results of their respective worldwide campaigns and detailed them out into a comprehensive history of the phases of the campaign.
While these are not quite as detailed as the Forge World books that came after them they were top of the line during that time period. As a precursor to the Imperial Armour books they do share numerous similarities such as the system overview pages, a brief out line of major conflicts and supplemental art showing modifications to standard kit that happened over the course of the campaign. The only thing the Black Library versions lack are army lists, which to be fair are published in the regular codexes at the time as they are "modern" conflicts.
If you'd like to pick up your own copy of either of these books click here.