Media has been used as a tool to influence opinions and perspective regarding certain issues and prioritize some ideas over the others. It is human psyche that when something is repeatedly told to a person, he or she starts to believe it without much logical thinking. At times one starts believing in something as result of media propaganda that seems irrational otherwise.
In the course of history media has been used as a very practical tool to influence public opinion. For instance in the 1930s Hitler used it successfully to further his Nazi movement. He made the Germans believe that they are super humans and are entitled to rule other nations. He urged them to face the other European nations who had inflicted a huge defeat on them in the WW-I, using successful propaganda through media.
The role of media propaganda as a tool to influence public opinion during the cold war was used by the USSR and USA extensively. Partially it was the advanced media of US that led to the supremacy of US in the cold war, eventually. Especially the role of media in Afghan war cannot be ignored.
In modern times the rise of Islamic fundamentalism in the aftermath of 9/11 has much to do with media though it had been existing for a longer period of time. But no one knew about it until it came in the lime light and got media attention after the 9/11 incident. Moreover due to the mega incident of 9/11 and some more related incidents terrorism is associated with Muslims though there are many other fundumentalists and terrorists who are inspired religiously or ethnically. For instance, the Shiv Sina and Vishua Hindu Pareshad in India burnt alive Christian missionaries in 2001 and thousands of Muslim in 2002. But since the world media does not give much importance to them and people around the world know less about them.
The public opinion moves around and is shaped by some powerful media groups around the world. These group bring those issue to public notice in which they feel there is some strategic and financial interest of their own and their preferred corporate groups on which they feed.
Regardless of its negative impacts media propaganda has served some noble causes for mankind. For instance media was the major force behind civil rights movement, equal rights for women rule of law and democracy, in the US and other parts of the world. And even today in certain corners media serves that purpose especially in the countries and societies where the media is free. It has contributed to tobacco free world fund raising awareness about environmental issues and aids etc.