In order to come up with the main themes, I suggest that you search for books and articles that are about the invention of the radio. When was the radio invented, anyway? I remember reading that the television was invented in the mid 1920s, so the radio must have come well before that.
In your class, did the professor asign a reading about this topic? Also, do you have any good books and articles to read in order to prepare to write this? If so, you can see what the other writers used for topics. After you read three or four articles about the advent of radio communication, you will have developed your own opinion, your own feel for how it affected international communication.
So, the good thing to do is to search your library or the Internet for articles about "invention of the radio" and "the history of international communications."
You will take some notes as you read a few articles, and soon you will find that writing the paper is as easy as talking about it with a friend. When you find some good articles about the invention of the radio, and HOW IT WAS USED in international communications, and WHICH COUNTRIES FIRST USED IT, and WHEN WAS IT FIRST USED IN WAR and, most importantly, you will learn about interesting themes associated with this topic as you read what other people have written about it.
Just remember to cite your sources. And when you find a few good articles and write a few god paragraphs, post them here for us to see. Good luck! I hope you enjoy researching this interesting topic.