The immediate cause of the Seven Weeks'…

The immediate cause of the Seven Weeks' War between Austria and Prussia in 1866 is Prussia's desire to annex the Duchy of Holstein.

Austria and Prussia had together fought a brief war against Denmark in 1864 to secure the predominantly German duchies of Schleswig and Holstein for Germany.

Pending final decision on their future, Prussia had taken control of Schleswig, and Austria had taken control of Holstein.

In April 1866, however, Prussia plots with Italy to wage a two-front war against Austria that will enable Prussia to gain Holstein and Italy to gain Venetia.

Although Austria tries to keep Italy out of the war through a last-minute offer to surrender Venetia to it, Italy joins the war with Prussia.

Austria wins key victories over Italy but loses the decisive Battle of Königgrätz (Hradec Kralove in the present-day Czech Republic) to Prussia in July 1866.