Oktoberfest was cancelled in 1866 because of the Austro-Prussian War.
The conflict, also called the Seven Weeks' War, pitted the Austrian Empire and its allies against Prussia and several German states, including Bavaria. Because Bavaria was involved in the war, Munich's large public festival did not take place that year.
The cancellation was one of several interruptions in Oktoberfest's 19th-century history. Cholera epidemics caused cancellations in 1854 and 1873, while the Franco-Prussian War led to another cancellation in 1870. These interruptions are why the festival's modern annual run is not entirely unbroken.
Oktoberfest began in 1810 as celebrations surrounding the marriage of Crown Prince Ludwig of Bavaria and Princess Therese. It was held on fields outside Munich, later named Theresienwiese after Therese. The name “Oktoberfest” can also be misleading today: since 1872, the festival has generally been moved earlier into September to take advantage of warmer weather, with only its final days falling in October.