The next wave of U.S. mergers may be coming to a shopping mall near you.Washington Prime Group Inc., a Bethesda, Maryland-based owner of strip shopping centers and regional malls, agreed last month to buy rival Glimcher Realty Trust in a $4.3 billion deal. Washington Prime Group Inc., a Bethesda, Maryland-based owner of strip shopping centers and regional malls, agreed last month to buy rival Glimcher Realty Trust in a $4.3 billion deal.