Why were the Detroit Red Wings in the western conference?

The reason is simple initially there were only 6 teams in the NHL and Chicago which as of 2014 still is in the western conference along with Detroit were the furthest west out of all 6 NHL teams which at that time included the Montreal Canadians, the Toronto Maple Leafs, the New York Rangers, the Boston Bruins, the Chicago Black Hawks and the Detroit Red Wings.

The mini story of the Original Six

The original six as their often called initially were all located in the eastern conference until the 1974 season when The East Division became the Prince of Wales Conference consisting of 2 divisions the Adams Division and Norris Division. What is called The West Division as of 2014 was at that time called the Clarence Campbell Conference and this conference also had two divisions the Patrick Division and Smythe Division. The Detroit Red at this time were in the Norris Division. In 1993 the NHL changed the names of the conferences to the eastern and western conferences. The Detroit Red Wings and the Chicago Blackhawks got put in the western conference.

The Detroit Red Wings are back in the Eastern Conference in the 2013-14 season moving forward

Because of their western conference schedule and generally to make travel easier for all NHL teams the Detroit Red Wings have moved back to the Eastern Conference in the 2013-14 season. Currently the Red Wings are in the Atlantic Division of the Eastern Conference in the NHL