Volume 1 to 4 cover the first world war from the perspective of the allies and the western and mediteranian front, including the Dardonelles and Gallipolli. Volume 5 is based on diaries and records from the Russian. German and Austrohungarain perspective and how it fitted in with the Allies actions. It is very interesting to see the things that we did not know at the time, the other nations that suffered at the hands of the Axis powers and the tactical successes and failures in various campaings. Why did some Generals have such influence over their leaders, why some of them decided to attacks at some places and not others.
Churchill studied this era and learned from past mistakes and successes on both sides, to become the great leader and saviour in the 2nd World War. I also recommend his Early Life book, and his account of the WWII. Despite his reputation for being terse and bad mannered this does not come across in his account. in WWII his relationship building and friendship were a major factor in the successful coordination of the Allied action, where fighting on several fronts at once the Axis did not gain superiority.