The United States lands in a four-way tie for spots 9-12 on the list, with an annual divorce rate of 2.7 per 1000 people. In the U.S., Nevada has the highest divorce rate of any state at 14%.
worldpopulationreview.com
Clearly divorce rates aren't correlated.
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The US has the highest rate of children living in single family homes but the difference is marginal. There are several countries that are within a few percentage points, and none of them have anywhere close to the same level of school shootings.
Single parent household rates have also generally declined since around the mid 90's with no correlated decline in school shooting events. In fact they have trended upwards.
The divorce rate / single parent household talking point is an idiotic attempt at obfuscation. Anyone with a functioning brain can figure out that school shootings are much more prevalent in the US primarily because of us having the highest rates of gun ownership in the world with generally lax regulations restricting access to who can own/access firearms.
Every country has troubled teenagers and children growing up in rough households. This is the only country on the planet where those kids regularly get access to firearms and murder their classmates en masse. No other country is even remotely close.
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TL;DR version:
@nctransplant is an idiot.