@SeaGreenEyez While studying this terrible phenomena, we (UK/Scottish students 2017-19) came up with two major factors allowing this to commonly occur in the USA.
Firstly that it is acceptable to employ lethal violence where and when an individual wishes to settle 'scores'.
Secondly, the availability of weapons which can cause lethal wounds on an extensive scale.
Simply put. Anger+Violence+Guns= Mass Shootings.
Rights are not god given (hahahaha) they are man made and therefore can be taken away. The Second Amendment is just that, an amendment. So if society wants, hold a referendum on gun control with at choice of three answers - two will give a pure binary outcome and partizan reprisals afterwards.
If the vote demands control, then that is what must happen.
Should it make a difference, Britain no longer has an Empire and we have far more fear of American invasion than the other way around.

@SeaGreenEyez I have a better knowledge and perspective on this than probably the majority of Americans.
From the weapon side of things, I can load and fire about four rounds per minute with a musket and can hit a standing man sized target at 50 yards most of the time. I have studied warfare both as an amateur historian and as a professional and can compare the modernising of weapons over human history.
Then as a Social Scientist where the USA, it's history, politics and sociology formed a major part of my recent studies I can see how the Constitution must continue to evolve under the guidelines that John Locke left.
In part a well related militia, was to prevent the rise of an internal Oligarch from becoming 'King'. Thus, the likes of Trump is what is meant to fight against. However, the War between the States 1861-65 pretty much destroyed the reasoning of this, as had the weaponry evolution from muzzle loading muskets to magazine fed repeating rifles.
Since the birth of the USA, the idea of the Nation State has risen and become the norm, and with it the need for well regulated national military accountable to the state and out with by international laws.