Following the market turbulence of the 1990s financial crises and September 11 attacks on the U.S. in 2001, financial integration intensified among developed nations and emerging markets, with substantial growth in capital flows among banks and in the trading of financial derivatives and structured finance products. Worldwide international capital flows grew from $3 trillion to $11 trillion U.S. dollars from 2002 to 2007, primarily in the form of short-term money market instruments. The United States experienced growth in the size and complexity of firms engaged in a broad range of financial services across borders in the wake of the Gramm–Leach–Bliley Act of 1999 which repealed the Glass–Steagall Act of 1933, ending limitations on commercial banks' investment banking activity. Industrialized nations began relying more on foreign capital to finance domestic investment opportunities, resulting in unprecedented capital flows to advanced economies from developing countries, as reflected by global imbalances which grew to 6% of gross world product in 2007 from 3% in 2001.