1921-22 was the Regina Capitals' first season in the new Western Canada Hockey League, they finished second overall and then upset the Edmonton Eskimos in the playoffs to win the league championship. Winning the league championship meant that the team had to face the winner of the Pacific Coast Hockey Association (PCHA) before being able to challenge for the Stanley Cup. Unfortunately, the up-start Capitals lost to the Vancouver Millionaires of the PCHA. Vancouver went on to face the Toronto St. Patricks of the National Hockey League (NHL), but would lose the best-of-five series for the Stanley Cup 3 games to 2.
They finished second overall in each of their first three seasons, with their third season only one point behind first place, but that first season would be the only one in which they would win the playoffs and advance to the next series. After three seasons well above .500, they fell to last place overall in their fourth season (1924–25) with only 8 wins in 28 games.
The Capitals tried spending their way out of their difficulties, but that only caused more problems. With the team in debt and losing money, they followed the NHL's example of heading south across the border and moved to Portland, Oregon for the start of the 1925–26 WHL season. The Regina Capitals renamed themselves the Portland Rosebuds, which was a rekindling of an older, then defunct, team from the PCHA. With that move, they became the only United States-based team in their league. Since they moved to the States, the league had to change its name to reflect that not all of its teams were based in Canada anymore. So, the "Canada" part of the league's name was dropped and it was renamed the Western Hockey League.
The move didn't help the on-ice performance of the team very much. They didn't finish last overall, but with an extra eight games played from the previous season, they only managed to better their total wins by 4 giving them 12 wins in 36 games.
After that season, the Western Hockey League folded. The National Hockey League bought every contract of ever player from the WHL for $258,000. The former Capitals/Rosebuds players would go on to form the nucleus of the expansion Chicago Black Hawks franchise, which began play the following season.