<Tr> <Td_colspan="2"> <Ul> <Li> Mysunde </Li> <Li> Danevirke </Li> <Li> Sankelmark </Li> <Li> Jasmund </Li> <Li> Dybbøl </Li> <Li> Fredericia </Li> <Li> Heligoland </Li> <Li> Als </Li> <Li> Lundby </Li> </Ul> </Td> </Tr> <Ul> <Li> Mysunde </Li> <Li> Danevirke </Li> <Li> Sankelmark </Li> <Li> Jasmund </Li> <Li> Dybbøl </Li> <Li> Fredericia </Li> <Li> Heligoland </Li> <Li> Als </Li> <Li> Lundby </Li> </Ul> <P> The Second Schleswig War (Danish: 2 . Slesvigske Krig, German: Deutsch - Dänischer Krieg) was the second military conflict over the Schleswig - Holstein Question of the nineteenth century . The war began on 1 February 1864, when Prussian forces crossed the border into Schleswig . Denmark fought the Kingdom of Prussia and the Austrian Empire . Like the First Schleswig War (1848--52), it was fought for control of the duchies of Holstein and Lauenburg, due to the succession disputes concerning them when the Danish king died without an heir acceptable to the German Confederation . Controversy arose due to the passing of the November Constitution, which integrated the Duchy of Schleswig into the Danish kingdom in violation of the London Protocol . Reasons for the war were the ethnic controversy in Schleswig and the co-existence of conflicting political systems within the Danish unitary state . </P> <P> The war ended on 30 October 1864, with the Treaty of Vienna and Denmark's cession of the Duchies of Schleswig, Holstein and Saxe - Lauenburg to Prussia and Austria . </P>

Why did prussia and austria attack denmark in 1864