Hi Jessie
The history of salsa is an
incredibly controversial subject so I think you would do best to try to reflect the controversy rather than try to be too definitive from what will have to be fairly sketchy research.
Here is a page demonstrating the wide range of opinions among Latin-americans themselves:
http://www.latindance.com/history_of_salsa.htm
The book The Latin Tinge by John Storm Roberts is a fascinating overview on the impact of Latin-american music on the United States from the 19th century up to the middle of the 1970s.
The book The Essence of Afro-cuban Percussion and Drumset by Ed Uribe has an interesting section of background and history.
Here is a salsa history from a New York perspective by Izzy Sanabria:
http://www.salsamagazine.com/generic.jhtml?pid=5
It's a huge subject so, after reading a bit, pick your aspect and don't get overwhelmed.
Hope this helps to get you started, let us know how you get on.