The 24 hour news cycle started rising in the late 80's. Most people think of the current pace of mass shooting incidents as having started less than ten years ago.

If you look at the chart you can see that the rise also began around the 80s with a few obvious dips every few years (especially post 9/11 when all sides where more focused on the middle east and less on each other). What's more it's not like they started off as mouth pieces (or at least as bad as they are now) they've been gradually taking sides over the years and it wasn't till the last 10-15 years that they really began reporting almost strictly one sided stories, heck it wasn't that long ago respected reporters in both fox and cnn started leaving their respective news stations because they couldn't stomach what they were being forced to report anymore.

what about the onslaught of social media?

Every country in the world has social media. If your thesis asserts that the underlying cause is something that is not unique to the United States, it CANNOT be correct.

fluoridated water then?

Australia, 80% of the population drinks fluoridated water. Zero mass shootings. New Zealand, 62% - about the level of the United States; one mass shooting. Republic of Ireland, 73%; last mass shooting there was 1998.

United States, 64%, 249 mass shootings and counting.

Are you seeing how this works?

so it's white people?

Are you even listening? It is something that the United States is either doing or not doing in particular.

In a way social media does have an effect (it's not the smoking gun per say but it is agitating the issue) Namely 2 major things influencing the issue.

1. search algorithms, while they help you find things you enjoy easier when it comes to political issues they tend to box you into echo chambers only giving you the information you want to hear and completely blocking out consenting voices. Worse since anyone can post anything they want, fanatics on both sides can make up what ever they want and unless you're willing to go out of your way to confirm if it's true or total BS most people will just accept it especially if it's what they want to hear.

2. the whole copy cat/ 15 minutes of fame issue. People for what ever reason decide they want to go out in a blaze of glory and see how others have done it before them on news/social media out lets and decide to do the same, either hoping for their 15 minutes of fame or hoping to make a statement to get others to follow what ever ideal they happen to be obsessed with

Then why is it happening in the United States and not almost everywhere else?

a lack of gun laws, mostly due to every politician being in the pocket books of the NRA. The growth of extremism on both sides of the political spectrum making people act out more irrationally (see 1. of previous post). Gay rights vs Christian Dagma reaching a head with both sides choosing a side and sticking by it at all costs regardless of whether it actually follows their ideals simply because the other side opposes them. The US has just become a perfect shit storm of side A vs side B and unfortunately as my meme was saying the news media has become little more than a political mouth piece and entertainment show more interested in ratings than informing. To quote one Fox news host when he left the station "I couldn't stand working there anymore. They were tearing this nation apart and all the higher ups could talk about is how great it made the ratings."

There's gay rights versus Christian dogma fights going on in the UK. No mass shootings. Poland - the government is egging on that exact fight right now. Canada, Australia, these countries are having the same experience. Corporate media is a toxic influence everywhere.

But the USA is the one where people just start shooting people every week.

The only factor you have listed that the United States exhibits that the other countries do not is the gun politics.

try them deep fried sometime, covered in a caramel sauce.