Would Austria ally with France ?
One of the - perhaps the single - most important influences on the period and events in question, is that, at the time, it was generally
assumed that France would win any war between France and Prussia.
This is a real problem for Russia, vis a vis fighting Austria, in a Franco - Austrian war against Prussia (1870). Hindsight can muddy our
understanding of the past.
Consider the likely scenario as it might have looked to Tsar Alexander II, Russia declares war on Austria in support of Prussia.
France trounces Prussia, Russia now faces France and Austria, the Ottomans step in against Russia - Britain perhaps acquiescing in this.
The spectre of Polish Nationalistic hopes rises, fanned by the hopes that France will assist. ( True there is a tension with Austria here). This
is a death knell for Russian hopes in the Balkans.
Consider Austria's position. Italy's rise in the 1860's is a very real threat to her important adriatic terrortories. There is the growth of Slav
nationalism, and the recent Hungarian uprising has threatened her very existance. These problems are not decisive if France defeats
Prussia, however Napoleon III has not been a reliable ally or friend to anyone. Will he abandon Austria for the sake of his own secret
machinations ?. Austria, having suffered at his hands in 1859 and 1866. This is one of the real problems for an Austrian attack on Prussia
(1870), that Napoleon III is an unreliable ally for Austria. The only certain thing the Austrian's can rely on is that Prussia will not attack them.
This at the time for an Austria that had been pretty battered over the last 10 years must have seemed like something to be protected.
Granted had Napoleon III been less Machiavelian, more reliable and less manipulated by Bismarck, then theres every chance Austria would
jump at joining France against Prussia.
Given the expeectation that France will beat Prussia, Italy will be wary of joining prussia.