gelding aggressive towards pasture mates

Question
I have read the notification.
My 28 yr old gelding (2nd in pecking order) has been turned out 24/7 with a 16 yr old gelding (top in pecking order) for the past 1 1/2 years and now the the younger gelding 2 weeks ago showed very aggressive behavior towards my horse by chasing him to the point that my horse had a pulmonary hemorrhage. (I saw this as I went to bring them in for dinner, when just 15 minutes earlier, they were happily grazing) Since I did not want the possibility of this happening again, another older 25 yr old gelding (lowest in pecking order), who had been turned out with both horses in the past but recently has been turned out with a young (very easy going)horse new to the barn (his owner was not comfortable adding him to the herd), was then turned out a week ago with the 16yr old gelding to see if they might be better turn-out buddies and within less than 3 minutes, was chased as well...right through a fence! Thankfully, that horse was not hurt but the aggressor unfortunately, sustained a stifle injury from the hard running and slipping on the wet pasture. All of these horses have been turned out together as a herd happily for the past 1 1/2 years,(another horse (who was 3rd in pecking order) was with them for 1 year but has since left the property 3 months ago).  So the established herd was broken up into 2 herds of 2 but all horses are able to see each other and "hang out" together as they have access to their stalls 24/7. What I'm wondering is why, after all this time, has the 16yr old now become aggressive? Is it because he has lost a member of his herd to a new companion and he's angry at his old herd mates? With the 16yr old now stall bound (probably for a long time), and the new horse has been turned out separately with both older horses with no issues, when would be a good time to try turning the 3 horses out together? Should we wait awhile for things to calm down? BTW - none of these horses are on high grain diets. 3 are "easy keepers" mainly getting a vitamin/mineral supplement and my horse gets a no-grain complete feed along with rice bran and joint supplement plus they get good grass hay. I would appreciate any ideas/in-put you may have. Thanks!

Answer
You question should be a list of what NOT to do with a horse - way too much going here for me to fix in an email and the fact you are asking tells me you have not read my website or watched my videos.

this is NOT a horse problem, it is a human problem. I talk about this on my site with is 500 pages long so there is not way to condense that into an email answer.

it would be like asking a home builder, I want to build a horse and can you tell me how?

I suggest you invest time in reading my site, watching my videos or you can keep asking questions on the internet until someone gives you bad advice until you or your horse gets hurt.

It is up to you what you , putting out my website and videos are free and available so all it takes is for people to take the time to watch.