Complex sentence: The project started in July 1999 with 21 participants, but by the 2010 event, over 200,000 people took part and wrote a total of over 2.8 billion words.
Split into simpler sentences: The project started in July 1999 with 21 participants. By the 2010 event, over 200,000 people took part and wrote a total of over 2.8 billion words.