The Dukes of Brandenburg and Neuburg sign the Treaty of Dusseldorf
for mutual defence against the destructive forces of the Thirty
Years War.
Citation:
Editors. "Treaty of Dusseldorf".
The Literary Encyclopedia. First published 01 February 2011
[http://www.litencyc.com/php/stopics.php?rec=true&UID=15919, accessed 19 May 2013.]