Why is terrorism so widely effective these days? It’s got a lot to do with mass media. Terrorists and rebel movements have become more common and deadly in the last few decades, and this is partly because mass media has, since the Internet arrived, become a lot cheaper. Getting the message out was always a problem for those trying to overthrow an unpopular government or even a popular one. For thousands of years most people were illiterate and the only way you could persuade them to join your cause was via person-to-person contact. Over the last two centuries there has been a huge explosion in literacy. Until quite recently (the 18th century) only a few percent of the global population was literate. What communications did exist were controlled by governments. But once ten percent, then twenty, then more than half of populations became literate, it was easier to spread your message. Those who could read could pass on what your printed, or even hand written, letters and pamphlets had to say.
Mass media first appeared in the mid-19th century with the development of the steam press, which made cheap-enough-to-reach-a-mass-audience newspapers possible. Editors quickly learned that FUD (Fear, Uncertainty, and Doubt) sells best. Politicians, rebels, and even advertisers found that FUD was a very effective tool to grab attention and change attitudes.
Put another way, excitement sells, and the best way to excite readers is to scare them. Modern terrorism, based on using murderous mass attacks on the public to trigger a flurry of media coverage, came out of this. The 19th century anarchists, followed by the Bolsheviks (communists), several fascist movements (like the Nazis), and many others, all used this media proclivity to jump on terrorist acts in order to scare readers into buying more newspapers. The terrorists got the publicity and attention they wanted, which sometimes led to acquiring political power as well.
It wasn't until television news became big that most newspapers stopped printing multiple editions each day. You could sell individuals several editions a day if you had a really hot story. Scary stories were, and remain, the best kind of stories. Radio appeared in the 1930s and this made it even easier to reach literate and illiterate populations. Combining radio and FUD allowed communism and fascism to spread far and fast in the 1930s.
The sad fact is that this situation is not unknown among journalists. Many of them have been complaining about it for over a century. No one has been able to come up with a solution. Good news doesn't sell. And the pursuit of scary headlines that do has created a race to the bottom. It's probably not much consolation but it wasn't always so bad. For example, see what happens when you report a great historical American military victory, like the 1942 naval Battle of Midway, in the style of today's journalism. Pretty sad. There are similar "comic" bits like that (on the web) covering other World War II victories. At the time, those victories were reported quite differently. Journalism has changed a lot in sixty years. But in many ways journalism has not changed. Editors and reporters still know that they have to either scare people or find another line of work. Fear sells but over the generations more scary stories have to be invented because so many people have built up an immunity to what scared their grand-parents.