Snow Elves although I cant really outright condemn either side since we know next to nothing about the events that started it. Other then a group of Mer either Falmer or Dwemer sacked saarthal. As well as whoever attacked it also had a working knowledge of its layout.
Also assuming it actually was mer since there were only 4 survivors, Ysgramor and his sons and Azhidal who wasn't there at the time. Although seeing as he was learning from the various groups of Elves at the time he very much could have heard rumors circulating around about it.
I just wish we had a better time line for the war with the Falmer and the Nords war with the dragons and Dragon cult. They both seem to have happened between 1E 1 and 139.
http://www.uesp.net/wiki/Lore:Skorm_Snow-Strider%27s_Journal