Well, let's define some terms. Certainly if someone you know dies in an attack, it's pretty significant. If there's a high body count, it's pretty significant. However, that's not what I meant. I meant a coordinated attack that is part of some sort of operation, as opposed to an individual who conceives of an attack all by himself. So, using that definition, when has there been that sort of significant terrorist attack in the US? Even Tim McVeigh and his cohorts just barely manage to be on the fringe of that definition. Of course, there's 9/11. Anything else?
You clearly don't understand how terrorism works. 9/11 was an anomaly, it's not even remotely characteristic of terrorism worldwide, let alone in the US. It was unprecedented in size and scope, and extremely unlikely to ever happen again.
You're clearly redefining terms to suit your predetermined outcome, rather than using standard definitions to understand the scope and reach of the problem. I'll stick with the definitions that the experts used. Any terrorist attack that can be classified as a "mass murder" is significant; because that is what terrorism has always been, throughout history, small attempts at mass murder by a few individuals, sometimes affiliated with larger organizations.
Terrorist organizations are not the big, shadowy corporate entities you seen in James Bond movies. They're loose affiliations of people with a common aim. Traditionally the structure of the largest terrorist organizations has been a single person (usually a charismatic religious or political leader), and/or a small coterie of officers/lieutenants, rarely more than a dozen or so. These leaders recruit a handful of operatives directly, or a handful of regional leaders who recruit a handful of operatives each. All organized in a cell structure, with cells typically limited to around 3-4 people. Such an organization, if bankrolled by a national government (such as Iran) or a particularly wealthy individual (such as bin Laden and Al Qaeda) can run up to a few hundred people worldwide.
Domestic terrorist organizations are nowhere near that large. the overwhelming majority of terrorist attacks manage a dozen or two victims. The rare larger attacks involve highly specific types of attacks targeting highly-concentrated groups of victims, such as airplane bombings. These types of attacks are becoming increasingly rare, as targets are hardened, and tactics change.
As has been pointed out multiple times, that's the old model of terrorism; a model which has been changing rapidly. The old organizations are becoming less effective and less important. The new face of terrorism is becoming increasingly dependent on the stochastic model for inciting and recruiting, so you're very rarely going to see anything on the level of any of the bigger historical attacks, which are not that common.
Historically, there have been less than 30 total attacks in the last 50 years
worldwide which claimed more than 200 victims per incident. The overwhelming majority of these have been airplane or train bombings; paramilitary groups in war-torn regions like Syria, Iraq, or Somali; or militant uprisings in developing nations like Nigeria, Chechnya, or India. In fact, the overwhelming bulk of the biggest terrorist attacks in the last 50 years have been these militant uprisings and paramilitary actions in the developing world.
In fact, even for attacks claiming over 100 people, in the last 50 years there have only been 6 that occurred outside of a developing nation and/or war-zone, or were not linked to separatist uprising (eg, Chechnya, Sri Lanka, Nigeria, Iraq, India, Russian-occupied territories, Pakistan, etc.).
Of those 6, two were airline bombings, one was the 11/15 Paris attacks, one was the 2004 Madrid train bombing, and the other two were Oklahoma City and 9/11.
By comparison, the various right-wing extremists don't kill as many, but there have been over a dozen such attacks in the US the last two years alone. And the number of attacks has been steadily increasing year over year since 2016, both in the US and worldwide. So far the Christchurch shooting has been the largest, with 51 victims total, but the body count continues to rise while the US government does nothing to stop it, and even refuse to acknowledge it's existence. The problem is only going to get worse, and it's only a matter of time before another Oklahoma City happens. There's a good deal of evidence that if Trump does not get re-elected next year, that there will be a wave of white supremacist terrorism erupt nationwide (he's certainly doing all he can to encourage it).
