Complex sentence: In 2007 he announced he had become a member of attac network, this happened weeks before the 2007 G8 summit, which Germany, holding the 2007 G8 presidency, was hosting.
Split into simpler sentences: In 2007 he announced he had become a member of the attac network. This happened weeks before the 2007 G8 summit, which Germany, holding the 2007 G8 presidency, was hosting.