Complex sentence: The American Funds, managed by the Capital Group Companies was as of June 2007 the largest family of mutual funds in the US, followed by The Vanguard Group and Fidelity Investments, with roughly $1.3 trillion in assets under management.
Split into simpler sentences: The American Funds, managed by the Capital Group Companies, is the largest family of mutual funds in the US, followed by The Vanguard Group and Fidelity Investments. At the beginning of June 2007, the American Funds had roughly $1.3 trillion in assets under management.