I have found two good articles.
One of the articles is written by Charlie Hore who is a author of the book, The Road to Tiananmen Square(Amazon).
Another one is about the very first demonstration, 11 March 2008. This article describes what happened there in chronical order. It shows it was a peaceful anniversary march.
I also have found a specific information about the forced contract between China and Tibet in 1951: 'Tibetan Agreement on Measures for the Peaceful Liberation of Tibet, [17-Point Agreement of May 23, 1951]"