The list of the Dallas Cowboys biggest rivals has been a changing conversation over the years. For a long time, the top answer was their NFC East brethren Washington. Dallas and Washington have played some all-time classic games in the NFL and in the day it was considered THE rivalry in the NFL (at least that’s what Dallas and Washington fans believed). Over the years, though, the significance of that rivalry waned as both teams went through some tough times when the wins were hard to come by. Lately, the Cowboys have been making it a one-sided series by dominating the last decade or so.