The Seattle Sounders–Vancouver Whitecaps rivalry is a deep-rooted Pacific Northwest soccer feud that began in the 1970s North American Soccer League (NASL), with both clubs founded on the same day in December 1973. It moved to Major League Soccer in 2011 and is a central part of the Cascadia Cup, a trophy shared with the Portland Timbers that has been contested since 2004. The rivalry is fueled by strong cultural ties and massive traveling fan bases, as recalled by former player Alan Hinton, and featured a record crowd of 60,342 in 1983. Although Vancouver led the overall NASL series 16–11–2, Seattle won all four postseason matchups, and the competition continued through lower leagues like the WSA and USL before reaching the top flight. This sporting animosity mirrors broader Pacific Northwest rivalries, such as the NHL's Canucks and Kraken, making it a defining feature of the region's sports culture.