Peace negotiations aiming to end (what was later to become known
as) the Thirty Years War are renewed in Cologne and Hamburg. At
this point it had already been going on for two decades.
Citation:
Editors. "Peace negotiations are renewed in Cologne and Hamburg".
The Literary Encyclopedia. First published 01 February 2011
[http://www.litencyc.com/php/stopics.php?rec=true&UID=16134, accessed 20 June 2013.]