First I’ll direct you towards /u/sunagainstgold’s response here laying out why it is hard to compare the concept of “terrorism” across centuries – especially when it comes to evaluating the intentionality of an act: https://www.reddit.com/r/AskHistorians/comments/3svwi8/is_there_examples_of_what_could_be_called/

It is important that we think of terrorism in the context of a larger category of what people call “political violence”. Political violence is the purposeful use of violence to further or achieve political goals, and terrorism can be thought of as a subset of that which targets either governments or civilians with the intention to intimidate or coerce a policy or social change. You can read more about the varying criterion at the START center here, which include (paraphrasing here) 1) there must be a goal to the violence, 2) there must be evidence of intention to coerce or intimidate, and 3) the action must be outside the context of legitimate warfare. There are also some other criterion that typify our modern conception of terrorism such as that it must be undertaken by non-state actors. This is problematic because it excludes state-directed terror, but that a subject for the large literature within political science, history and national security studies that tries to narrow down exact what distinguishes it from other acts. There are also legal definitions, such as US law.

The point of that is to say that, since this is likely asked in relation to the Las Vegas mass shooting, it is important to distinguish between terrorism and mass casualty attacks that have no apparent intentionality to change the status quo, politically or otherwise. I don’t want to speak on the Las Vegas shooting, since it violates the 20 year rule and information on the shooter’s intentions is spotty now, but terrorism in the sense of an intentional act by non-state actors designed to create mass casualties and intimidation for political purposes has been around well before the 20th century.

One prominent example would be Guy Fawkes’ famous attempt to destroy the House of Lords in London in 1605. He was allegedly part of a conspiracy of Catholic radicals to kill King James I of England by exploding barrels of gunpowder during the House’s proceedings. It failed, but the intentionality of 1) using violence, 2) taking out prominent elites to intimidate or coerce a policy change and 3) sneakily using explosives to assassinate targets would I think put this into contention as a pre-1900 act of terrorism and political violence.

On the second kind of violence, which is not intended to change policies or the status quo in any purposeful way, I am much less qualified to say and will have to let someone else answer on that account.

I'm not sure if you actually mean terrorism or just random acts of extreme violence. There is a distinction, though where exactly it lies is up for debate. The problem with defining terrorism is one that's argued every day in academia, and any rigid definitional framework almost always has a glaring hole or two.

But what's most important is not having a very specific and thorough definition, but rather a definition that at least excludes enough to make the actions described by the word truly distinct, as the fact is that while scholars don't really agree on a precise definition, they all tend to identify the same sort of groups, people, and attacks as terroristic. So clearly, they're thinking about the same ideas... They just can't put them into words accurately.

Generally, to meaningfully distinguish terrorism from other political violence and other non-terroristic violence, it's good to ask three questions.

1. Are the perpetrator(s) motivated by a sincere belief that their actions could in some way spur political change?

2. Are they a part of an identifiable wider movement or group? It's probably not terrorism if it's a one-off thing, ie: the assassination of a political leader that isn't part of a wider trend of political violence.

3. Do they mostly target officials or civilians (including infrastructure) rather than the military? (mostly the latter would probably be an insurgency)

First, it's important to note that random mass killings, especially in the US context, are rarely terrorism according to this criteria. For someone "going up to a steeple and shooting random people", look at the Texas University tower shooting. Disturbed man with a brain tumor who felt compulsions to murder, definitely not a terrorist.

Now with that aside, to directly answer the question: a group that's often cited as a possible example of early 'terrorism' by scholars: the Sicarii, or Men of the Dagger, who resisted Roman occupation of Judea around 40-50AD by assassinating Roman officials and sympathisers with daggers. They were an organised group, part of a wider movement or sentiment (resistance to Roman occupation of Judea) with clear political motivations.

As far as terrorism as actually an identifiable phenomenon that's really distinguishable, it began with the Fenian movement for Irish independence in Britain, in the mid 20th century, who were, again, an identifiable group and part of a wider identifiable movement. They carried out some pretty devastating bomb and dynamite attacks in England, as well as a few failed uprisings.

But Anarchist terrorists in Tsarist Russia and Italy spurred the first truly global "wave" of terrorism. These groups believed that revolution was needed, and that the best way to spur it was through powerful symbolic attacks, such as assassinations of high-ranking political figures, which the people would see, realise that the power structures of society are not as strong as they seem, and rise up to overthrow them. The emergence of railroads was fundamentally important to this, as they enabled fast, far-reaching information dissemination that wouldn't have been possible otherwise. I do not know much about the early Italian anarchists, but the Russians made heavy use of the invention of dynamite, which was relatively easy to access and use with incredibly high destructive potential.

The most famous group from this period is probably Narodnaya Volya (People's Will), who are known primarily for their relentless campaign to explode Tsar Alexander II with dynamite. In audacious and unprecedented fashion, they successfully dynamited a train and the Winter Palace, but failed to get the Tsar in both cases. They finally managed it in 1881, by lining a road that he was travelling with a few men who were literally lobbing dynamite at his coach from close range. This was probably not the most practical method, especially since the bomber blew himself up in the attack (by accident), but they were going for high symbolism. As for why they popped up when they did, new technology really enabled their methods, which obviously would have been a lot harder with a bow, arrow, and horse - faster and wider dissemination of information, weapons with mass destructive potential such as dynamite that were a lot easier to employ than such weapons had been before, small, easy to conceal and easy to use handguns, etc, all of which were also being produced faster and easier than ever before due to the industrial revolution. Which itself also created the new societal relations that probably spurred Anarchist thinking.

The reason that the Anarchist movement was the first real "global" wave of terror is because the methods of the Russians and Italians were adopted all over Europe and the USA by other groups, disconnected from them but still influenced by their ideologies. Since then, we've had a few different globally recognisable terrorist movements. IE: Anti-colonial terrorism (Algeria, Angola, Mozambique), Nationalist terrorism (South Africa, Northern Ireland), Leftist internationalist terrorism (came from everywhere, but mostly fought for Palestine and also ransom money), and Islamic terrorism, which we're all familiar with.

In short, yes, there were definitely terrorists before the 1900s, but only in the 1800s. Before that, things get a lot more iffy, as terrorism as we know it is really a modern phenomenon. The word has only been in the lexicon since the French Revolution, and has only been used to refer to what we know as terrorism it since the second half of the 19th century, so the best way of applying the word is probably to simply limit it to acts that were recognised as terrorism even in their own time, rather than us applying our modern understanding of the phenomenon (which is informed by the extremely negatively connotations of the word today) and searching for movements and events to label as terroristic in the past. Even after that, distinguishing between terrorism, political violence and just plain violence is often blurry.

As a footnote, terrorism was not always a bad word in the collective consciousness - it used to be seen as a fairly noble means to an end. Vera Zasulich, who was on trial for attempted murder in 1879 in Russia, proudly exclaimed to the court that she was "not a murderer, but a terrorist." She was acquitted. Terrorist tactics have also been employed by plenty of movements that modern morality would consider legitimate, such as by the ANC in South Africa. It became a bad word (though not as bad as today, and it was certainly not entirely positive beforehand either) with the rise of leftist internationalist and Islamic terrorism, both of which have often been a lot less coherent in their goals and sensible in their methods, and it's really taken on a more callous character in the collective consciousness since, shown by the way anti-colonial and nationalist terrorists started distinguishing between terrorists and themselves, who were "freedom fighters".

I read an interesting paper on the history of terror as a means for political change some time ago. The idea is that terrorism as we has come in four waves motivated by distinct ideologies: anarchism in Europe and America, then Marxism in the same regions, then anti-colonialism in parts of Africa and Asia, and finally Islamic fundamentalism as we now know it.

Is anyone familiar with this idea? Is this a mainstream view? I haven’t been able to locate that source again.

I'd point in a different direction than most of these comments and suggest that modern day terrorism is part of a historical development of modern day warfare theory from a paradigm of Control Enemy Territory/Prevent Enemy Control of Our Territory => Inflict Damage on Enemy Population/Prevent Enemy Infliction of Damage on Our Population, to one in which damage can be inflicted without control of territory being a prerequisite. Thomas Schelling does an excellent job of discussing this in his book Arms and Influence examining the development in the context of the early atomic age.

Already in WWII this developed in American strategic bombing which leveled German and Japanese cities before the Allied armies occupied an acre of German or Japanese homeland. This was a sea change from historical warfare. The Mongols or the Romans, however effective, had to control a city before they could sack it or kill the population. If damage can be inflicted without exerting control, control and the land based mass military forces that it requires become less relevant than the apparatus that allows you to inflict damage. For powerful nation states these are bombs and missiles, for the guerrillas it is the terrorist bomber.

This resulted in the development of guerilla warfare theory by people like Mao in his Little Red Book and the leadership of the Algerian independence forces, with the emphasis shifting away from control of territory which would just provide bombers with easy targets and towards attacks on soft targets which could inflict damage without the need to exert physical control. These doctrinal developments were studied by revolutionaries the world over, and adopted.