On 1 August 1914 for reasons still debated today, the German Empire declared war on the Russian Empire to set off World War I. I’ve written about some of the battles between the Germans and Russians early in WWI here.

Map credit above: By historicair (French original)Fluteflute & User:Bibi Saint-Pol (English translation) [CC BY-SA 2.5-2.0-1.0], via Wikimedia Commons