The biggest producer of beer in American is Anheuser-Busch (AB). Formally the largest brewer in America, Anheuser-Busch is now part of the global beverage company InBev, the maker of approximately 200 brands of beer and soft drinks that primarily includes Stella Artois, Becks, Leffe, Hoegaarden, Skol, and Michelob. AB InBev, through its interest in Grupo Modelo, also offers the Corona brand. The company is valued at 130 billion dollars with revenues over 31 billion worldwide. The flagship product is Budweiser, the most popular beer brand in North America with a 20% market share along with Bud Light. Part of the reason for this control of the market is the complex system of distribution in the beer industry put in place since the end of prohibition. This system has enabled brewers to tightly control their distributors and in turn, distributors have control of their individual markets.
Before prohibition, brewers controlled their own bars. If you wanted Budweiser you had to go to a Budweiser bar. They provided the bar owners not only with beer but gave loans for furniture, beer equipment and other needs. They required the owners to carry only their brands. After the repeal of prohibition, states enacted strict laws to control the alcohol industry.
The three-tier system of beer distribution was developed. This is a 2-level vertical marketing system where the brewer awards a distributorship to a geographic area. AB does not sell directly to consumers; they sell Budweiser to the local distributor. This distributor knows their individual market, the local restaurants, bars, and retail locations and their needs.
This system has both benefits and drawbacks. Because each distributor is an independent company they can deal in quantities appropriate for their market. Proponents of the system argue that if direct sales of beer to retailers were allowed small firms would be at a disadvantage to large outlets such as Costco that can purchase in mass quantities and get the best price possible for Budweiser and push out the smaller or craft beers. Because all beer must go through a distributor, a single distributor can deal in multiple products, not just Budweiser and get more brewers on the shelves. The distributor helps the retailer reduced inventory costs.
Over the years, the distribution system has developed problems. AB distributors have had a reputation for pushing out smaller non AB products from shelves by threatening retailers that try to sell other products. They can reduce the availability of Budweiser, often the most profitable product. In 1997 AB had distributors sign an “exclusivity incentive program” which gave huge incentives to drop competitor products.
In an effort to compete more effectively, AB is attempting to buy controlling stakes in distributorships in some of the largest markets. Some states have modified their laws to allow this and AB is attempting to trip supply-chain costs. In this way Budweiser can get sold to the largest retailers directly from the brewer while the independent distributor can still provide service to the smaller restaurants and local bars.

Reference
Kesmodel, D. 2010. Anheuser Granted Partial Win in U.S. Court on Distribution. Wall Street Journal (Eastern Edition), p.B.8. Retrieved May 24, 2011, from ABI?INFORM Global. (Document ID 2132587221).
Kesmodel, D. 2009. Corporate News: Anheuser Weighs Change in Beer Sales, UBS Says--- Analyst Reports Brewer Is Considering Wider Ownership of U.S. Distributors, but Firm Plays Down Potential Shift. Wall Street Journal (Eastern Edition), p. B.3. Retrieved May 24, 2011, From ABI?INFORM Global. (Document ID 1759821841).
Kesmodel, D. 2007. Small Brews Shows They’re Not Weak Beer; As Popularity Rises. Specialty Brewers Challenge Distributors. Wall Street Journal (Eastern Edition), p. B.1. Retrieved May 24, 2011, from ABI?INFORM Global. (Document ID 1395708281).
Industry Center – Beverages- Brewers. 2011. Retrieved from Yahoo Finance: http://bizyahoo.com/ic/346.html Kotler, P., & Kevin, K. 2009. A Framework for Marketing Management. New York: Prentice Hall.
Spiess, D. 2009. How the Three-Tier Beer Distributor System Works. Retrieved from Fermentarium: http://www.fermentarium.com/industry/how-the-three-tired-beer-distribution- system-works/