Prussia is militarized by tradition. Just look at Voltaire's depiction of Prussia "An army with it's own nation" ... there might be colonial disputes, a border accident between Austria and Prussia, ... I'm wondering ... was Austria in Germany acting like Cold War US, very interventionnist ?
A post Sadowa effort to create an "Entente Cordiale" between France and Austria seems late to save France from a big fail in Sedan ...
So why didn't people see it as a threat before 1866 then if it was so highly militarized?
Answer? The spell of Prussian militarism on the thinking of Europe was broken at Jena by Napoleon. After that, who was going to regard Prussia as a threat just because of military tradition when it was so humiliated?
It would only be seen as a threat after it beat a significant great power on its own.
And that was only after Sadowa that the threat becomes perceptible by France and Austria. Before Sadowa, Prussia is seen as Austria's little brother, it's junior partner in the German Confederatrion.