Board Thread:Lore Discussion/@comment-209.7.3.188-20160303204000/@comment-26893431-20160313182400

Bronkiin wrote: Again, the opinion of one Imperial supporter. This is not sufficient evidence in its own right. This isn't even an opinion, if everyone still had their shrine of Talos than that isn't a bloody opinion. That is a fact.

Add that up with the fact that the Thalmor aren't recorded to have been in Skyrim prior to the Markarth Incident, it's more than enough evidence that Ulfric drew them there. Stormcloaks are always ignorant to that.