The slump in global stock prices could just be getting started as a few months of declines may not be enough to correct the years of booming stock prices, investment managers told CNBC.

Stocks ended mixed Monday, capping a dismal quarter and first half marked by rocketing oil prices and battered financials. The Dow is down 14 percent since the beginning of the year and ended the first half about 20 points from bear-market territory.

The Dow Jones Industrial Average, the most widely known barometer of the U.S. stock market, is making the first change in its lineup of 30 stocks in nearly four years, dropping Honeywell and Altria and adding Chevron and Bank of America.