By James W. Gerard, 1918
It is an absolutely necessary read to grasp and understand old Prussia and how Germany came out of the ashes of the first world war.
Readable? As fine of reading material that you can discover. It's written by the US ambassador who arrived in 1913, and watched the entire war adventure unfold. There are countess examples of German life, culture, and politics detailed in the book.
Several encounters with the Kaiser are given in fair detail, and you gain a great understanding to the operation of the government by the military figures of Prussia.
I would also suggest that you get a rare glimpse of what the Americans were seen as, and how many dynamics were thrown into action after the war.....barely changing the German government, and helping the Nationalists Socialists come to power.
The book is worth reading.