I believe Viennese waltz is the oldest of today's ballroom dances. Most credit it as having its origins in an Austrian folkdance; however, some say it is French or Italian. It became popular at the end of the 1700's. It was the first dance in upper society that used an "embracing" dance position, and was considered quite scandalous at the time.

I'm not going to do your homework for you; but you might want to talk about its history by tracing its introduction to different countries in Europe and being banned, the development of its slower version developing out of an Americanized version called the Boston, and the evolution of the other ballroom dances. You might even be daring and make some observations about the social upheaval at the time, such as the French Revolution and Monsieur Napoleon. There are several websites out there if you bother look, and probably several books at your nearest library. Have fun learning!