Researching fashion history is an interesting, absorbing and inspiring activity linked to all NC, HND courses as well as degrees and future careers. This 1800's, 1900's and 2000's timeline describes construction, silhouette and style feature changes. Although these are basic they are reasonable starting points for further research.
This fact monster fashion timeline fleshes out the years from 1858 to 2000. This timeline has both fact and illustration.
Fashion Era is a very comprehensive and well linked site. please explore.
Irina Ivanova is a popular fashion artist who has illustrated silhouette and style changes throughout the 20th Century here.
This wikipedia page is deep on fashion history fact and links too.
These are all just to get you started. Why not start a skydrive file titled fashion timelines? This will be a useful tool for many subjects and useful for years to come.