Even the Walter started the war between the worlds shocker wasn't one. It was either going to be Walter or Bell, since they created/instigated the tech to begin with. Now we just know (or assume at this point) it was over his kidnapping of Other Peter.
I'd say we already knew this as well; at least, that was my surmise from last season's finale, when we discovered that (A) Our Peter was dead, yet here's another; (B) there's another universe at war with us and; (C) the Manifesto of these cross-dimensional terrorists was written on Walter's typewriter--or, rather, Walternate's typewriter. Logical conclusion: Walter abducted another universe's Peter, and that universe's Walter founded a radical, scientific/terrorist movement to fight against such intrusions and take the battle to the other side.
But while it's nice to get confirmation of these things (I hate it when shows like the X-Files always leave things implied, so they can keep changing the scenario to shock the storyline into life), this episode really wasn't about the plot but the delivery. And it delivered well.
Fictitiously yours, Trent Roman