I am going to assume this question is talking about Europe.

The main differences would be technology and the spread of nationalism coupled with the idea that one could get rid of the ruler or change the system.

By the 20th century the idea of revolution was well known and constituted a pattern which could be followed. Imagined Communities by Benedict Anderson does a good job of explaining how the American and French revolutions were seen by contemporaries as models which could be applied to their own systems. Further me makes the point that the rulers were seen as part of the nationalist system and not above it. He considers specifically the case of the Kaiser, considered (? self declared) to be the 1st of the Germans he could therefore betray the Germans. He contrasts this to earlier rulers, how could Louis XIV (L'État, c'est moi) be considered a traitor to the French, the idea wouldn't even make sense in that context.

In this sense the state had to be worried about subversives in a way they were not in earlier eras. Sure regimes were overthrown before but it had generally been a system of "same ship different captain".

However, as Eugen Weber shows, in his Peasants into Frenchmen the modernization that took place between the 17th and 18th centuries and the 20th century, specifically during what Eric Hobsbawm called the long 19th century (1789 and 1914) changed society massively.

Roads and rails, standardized education and military service all had great impact on nations. Weber traces this as the change from local to national, very important when you want people to die for you in far away places. Obviously there were people who thought in a national sense before this but an important thing to keep in mind is that in the 17th and 18th century the majority of people worked in agriculture and lived in the countryside while in the 20th century they did not. More important than this demographic shift is the idea of the state entering into the conciseness of the population. A 17th century Bavarian peasant would have a very different worldview than a 20th century Bavarian farmer.

The state would have a monopoly on violence in the 20th century, see Politics as a Vocation by Max Weber, in a way they did not before.

Obviously the spread of radio was important as well, but its something I haven't studied.

The rise of a bureaucratic soceity where the government was able to keep track and organize large numbers of people. Witness the mobilizations of 1914 in Russia, something that would have been unthinkable the time of Peter the Great, or look at the attestation papers of Canadians in the Great War, obviously these types of documents were different than what Sir Issac Brock would have had available.

I would argue that the dictators had more actual ruling power due to technology and bureaucracy, but also had to be aware of the mood of the people since there could be a revolution against them. If they were more or less worried about this its hard to say and probably varied over time and space.