Long before television or movies, stage acting was the catalyst for a growing phenomenon of actors who worked on stages for famous playwrights such as William Shakespeare. Many interesting facts can be unearthed in regard to acting in his era. Even before the time of Shakespeare were the ancient Romans, who held battles in front of large audiences as a form of entertainment much like a modern-day play on stage for all to view. For your research topic, look into a subject such as "Stage Acting in the Elizabethan Era" or "Stage Acting Modernization for the 21st Century."
For almost as long as there have been performances in front of an audience, there have been people writing the script for the actors to follow. Many playwrights have had an enormous effect on the society of the world. Modern-day playwrights such as Arthur Miller have had almost as much influence over the actors who perform their work as Shakespeare did in his day. A possible topic for this category would be "The Most Influential Playwrights of the 20th Century" or "How Tennessee Williams Set the Stage for Modern Plays."
All good actors have methods they have used throughout their careers to make them become performers who people want to admire. It takes a great deal of practice and passion for a person to be able to change moods in an instant or create tears on cue, and many actors share their methods to accomplishing these goals. You may enjoy a topic such as "James Dean's Acting Method" or "How Method Acting made Marlon Brando a Star."
Costumes that are correct for the time period represented in the movie or play are very important. Audience members want to see actors who can correctly represent the era involved, and costumes are an easy way to accomplish this goal. Proper costumes and actors who can correctly wear and use them are imperative to good acting. "How the Right Costume Can Make or Break a Film" would be a possible topic that could lead in many directions.
When sound was introduced into films in the early part of the 20th century, the job of the actor changed greatly, causing a shift in type of actor needed. At this time in acting history, actors had to either change their acting styles, voices or mannerisms, or they would be replaced. Therefore, the acting styles of many were changed in order to keep the jobs that they so desperately needed. Reasons necessary for the changes could be shown in a topic such as "Greta Garbo: From Silent Films to Silver Screens."
Acting has changed over the course of time from mainly a hobby to a profession. Actors now not only have to entertain, but many also have to hold themselves to a higher regard in order to keep a healthy image for fans. You may want to research how the shift from hobby to profession played out, and the subsequent impact on actors.