Henning was the secretary of Gotthard Kettler, the last Master of the Livonian Order and the first Duke of Courland. His history of the Livonian War covers the period 1554-1590 from the point of view of a very well-informed but partisan observer.
Obtainable directly from the printer Kendall-Hunt, 4050 Westmark Drive, PO Box 1840, Dubuque IA 52004-1840.