The Battle of Jena was fought on October 14, 1806, in Jena, in today's Germany, and resulted in a French victory under Napoleon Bonaparte against the Prussians under General Hohenlohe.
Hegel, who was then a professor at the University of Jena, is said to have completed his chef d'oeuvre, the Phenomenology of Spirit, while the battle raged. Hegel considered that this battle was "the end of the history", in terms of evolution of human societies towards what we would call the "liberal democracy". More on that in Francis Fukuyama's book: The End of History and the Last Man.
See also: Battle of Auerstädt