Prussia, its other German speaking allies, and Italy defeated Austria in the Austro-Prussian War in 1866. No one came to Austria's aid other than France but it was too little too late. Fallout from the Austro-Prussian War led to Franco-Prussian War in 1870 which Prussia also won. With Austria and its only major ally defeated, it seemed like no one would or could stop Prussia's unification of the German speaking lands including Austria. So why did they let Austria remain independent?