The Mississippi Valley Sports Club was formed after the purchase of Tom Packs' wrestling
interests in St. Louis in June 1948.  At that point, wrestler
Lou Thesz owned 55% of the
new promotion, Bill Longson owned 35%, Toronto promoter Frank Tunney owned 5% and
Montreal promoter Eddie Quinn owned 5%.

But on paper, the corporate breakdown looked like this:
Mississippi Valley Sports Club in St. Louis
Martin Thesz became the "front" for the organization in the St. Louis market and the
promoter of record for all shows.  At that point, Lou Thesz was in the midst of a heated
war in St. Louis against rival
Sam Muchnick.  Muchnick, in July 1948, helped form the
National Wrestling Alliance, a cooperative union of bookers looking to better assist
each other in rivalries such as the one he was engaged in.  With assistance coming in
from
Al Haft in Ohio and Tony Stecher in Minnesota, Muchnick was looking to get an
upper hand on his enemy.

This wasn't a staged "war" as seen so many times in pro wrestling, but a serious
business conflict that would see the winner capitalize on the huge St. Louis wrestling
market.  There was a great deal of money on the line, and neither Muchnick nor Thesz
wanted to give up.

However, all things must come to an end one way or another.  Muchnick and Thesz
met in 1949 and figured out a way to meld their interests.  The St. Louis conflict
officially ended in August 1949 with the two men becoming even partners.  However,
another source stated that Muchnick held two percentage points more than Thesz.

To maintain the illusion of competition in St. Louis and to keep the integrity of the two
individual promotions, both the Mississippi Valley Sports Club (Arcade Building) and
Sam Muchnick Wrestling Attractions (Claridge Hotel) offices remained opened.  In front
of the public and other state officials, there was never a peace agreement.

Simply, Muchnick and Thesz didn’t want people to know that there was now a
monopoly over the booking and promotions of pro wrestling in the city.

Behind the scenes, the percentages of ownership of the company changed.  In
December 1955, Thesz sold out.  
Bobby Managoff owned a piece, and in 1972,
Kansas City interests were locked into St. Louis' wrestling scheme.

As for the Mississippi Valley Sports Club, it remained a separate entity until it "publicly"
merged with Muchnick in September 1959.  The St. Louis Wrestling Club was then
formed.