Terrorism is a tactic. It is not new. Terrorism is avoiding targeting military type targets (ie, military, federal security, government sites, etc) and instead going for wounding, maiming, and killing "soft targets" like schools, playgrounds, public venues, airports, and other non-military targets to create fear and terror to advance a cause. It is not protected by the Geneva Accords and is the same legally as piracy.

This isn't to be confused with insurgency, which can be legitimate warfare since people have a "right" to rise up against their government or against occupiers. Insurgency is a type of warfare, not a "tactic" like terrorism. It can be legitimate or not, just as warfare by a nation state can be legitimate or not (ie, "war crimes".) It is also not to be confused with asymmetric warfare, as all warfare has elements of asymmetric warfare, they just are not always a near-peer conventional fight.

History is full of nation states (or the predecessors, like city states) using terrorism to suppress and intimidate populations. There is a legitimate question of whether to weigh a historical event using modern rules and ethics, but that isn't your question. Unless you define your term as to what you mean by "terrorism" (if you do not mean the conventional technical term of it being a tactic of illegal warefare targeting soft targets to create terror to advance a political cause), it's hard to limit a well established tactic to a single period in history.

Thank you Bart Kemper for starting the conversation

The Geneva Convention has identified specific crimes as terrorism. For example, in Geneva Convention at the Conference for the Repression of Terrorism, article 1 defined terrorism as “acts against a state that would provoke panic and horror among certain persons, groups of people, or the public.

any way the term terrorism is used widely, there is no single agreed upon definition of the concept at either the academic or international level.

But the history tell us that the Terrorism is not a modern phenomenon, and that it has ancient roots that show terrorist acts dating back hundreds of years ago. In the first century A.D., the Old Testament (or the Torah) depicts a group of fanatics who terrorize the rich Jews who cooperated with the Roman occupier of the Eastern Mediterranean. During the Roman era, it was difficult to distinguish between political crimes and terrorism.

In fact the world came to know terrorism following the Roman era as a means used by the feudal lords in controlling their people and slaves. In the beginning of the seventeenth century, European countries began to dominate world's seas and with the increased volume of ships transporting goods through the east-west trade route, the phenomenon of piracy emerged. Since that time, piracy was considered a form of terrorism, and it has persisted into the twenty-first century. Thus, the practice of terrorism has been carried out in different forms throughout the course of history depending on the circumstances and parties involved.

Piracy is a criminal act, same a hijacking trucks. Most pirates did not go for notoriety as they wanted to be able to go on land and not be targeted. It is a profit motivation, not political one. The pirates of Tripoli were in it for the money, and the terror they caused was secondary, not their primary intent.