My "modern" may not be yours, bb! I'm not implying that everyone switched sides immediately when the Steelers began winning Super Bowls, but even the TV and radio priorities and affiliations in Eastern Ohio have changed from Browns to Steelers, over the years. In addition to the NFL, there are high school rivalries along the border, as well, in both football and basketball, not to mention OSU/Penn State in the Big Ten. But truly, at the root of enmity, is Browns/Steelers.
Geographical proximity plays a huge part - regional bragging rights and whatnot. Western Pennsylavnia and Eastern and Northeastern Ohio are the cradle of football, professional football in particular. Again, with the Browns and Steelers being the highest-profile piece of that. But save for Texas and, more recently, Florida, these states are also storied high school football bastions.
"Every game, every point is a necessity." -- Ty Conklin, January 2007
"I'll have a chance to compete for the post of first issue. This is the most important thing." -- Sergei Bobrovsky, June 2012
Didn't feel much of anything, but I'm practically in the basement over here. There was a little more rattling than usual, but that's all I noticed... until about five minutes later when Twitter started going a little nuts.