Now this is of course an opinion, so take this with a grain of salt and please state your opinion of what you think happened to Dutch. But in this post, I'll discuss what could have happened to Dutch that made him into the insane psychopath murderer and outlaw he was at the end of RDR2 and during the original Red Dead Redemption.
So, there are two sides of course to what could have happened to Dutch and it's those two that most people of course choose between. One is the "Dutch changed from a good leader with morals to a blood hungry murderer" and the other is "Dutch just showed his true colours, he was always like this and never a man of principle". Now, I have always been on the boat of Dutch having changed, but I have thought it through and I personally believe that it is a small mix of both. Dutch did have that darkness within him but he was always able to control his impulses and he always was a principled man who did believe what he preached to the gang. And one big part that always kept Dutch in check and challenged him was of course good ole Hosea.
Now, there are other reasons that I will delve into that could be a catalyst for Dutch changing and his dark impulses coming out more:
Blackwater: This is undoubtly what started his struggles. The Blackwater Ferry job is what started the downfall of the Van der Linde gang, and one major moment that occured here was Dutch shooting mother Heidi McCourt in cold blood during the robbery. The reason for this is unclear, but it could be that Dutch was stressed and pressured into killing him by Micah, as Micah was "pressuring Dutch to kill her". Or maybe Dutch did because he could, whether he knew the reason for it or not. Why he killed Heidi is unclear but it is clear that him killing her had a big affect on him in some way. And the massive gunfight did have a affect on Dutch too in some way.
Some in the gang beginning to doubt him: The gang had always been a firm believer of Dutch's ideals and always had faith in him (besides Micah of course). But during the game and even at the beginning in both Chapter 1 and 2, some began to show doubts after what happened in Blackwater etc. This of course affects Dutch because he can't handle people not having faith in his abilities to lead them. Those who began to show doubts first are Hosea and John (that I think of at least). So people beginning to be unsure and doubtful of Dutch seems to have a affect on him.
The Pinkertons on their tail: Undoubtly having the Pinkertons on their tail and the law in general now with his now massive price on his head might put tons of pressure and stress on Dutch, which seems to get worse overtime as the gang causes more and more noise in Blackwater, Valentine, Strawberry, Rhodes, Saint Denis and Roanoke Ridge.
Micah's influence: Do I even need to explain this? Micah's presence and influence is certaintly something that affects Dutch the worst way as Micah tries to push Dutch to indulge in his dark impulses of murder and chaos.
Gang members dying: I mean... when 5 members of your gang are killed within a few months, it's definitely going to mess with you a bit I feel like. I'm talking of course about Jenny, Davey, Mac, Sean and Kieran.
Head injury during trolly station robbery: Now, I don't think this is what caused Dutch to fully go crazy, as some would think. But I do agree that this potential head injury or concussion he suffered might have had a affect in his thinking and emotions after he, Arthur and Lenny fell into a trap by Bronte who betrayed them, something that pisses Dutch right off.
His brutal murder of Bronte: Now this is where Dutch's emotions, impulses and dark side shine through, when he brutally drowns Bronte to death and then feeds him to a alligator, a action shocking his proteges John and Arthur.
Hosea and Lenny's murder: Hosea's death and the bank robbery going completely wrong definitely affected Dutch so much, especially Hosea's death, a man he looked at as a best friend and brother, someone who always was there for Dutch, kept him in check and loved so much like a brother. Shot as a unarmed prisoner in a brutal way. Lenny's death didn't help either, as while Dutch didn't have like a strong relationship with Lenny like he had with Hosea but Lenny was someone Dutch liked very much, sort of like a young Hosea in a sense who challenged Dutch's views and Dutch's obsession with Evelyn Miller.
Time in Guarma: Dutch wasn't fully able to process Hosea and Lenny's death as he, Arthur, Bill, Javier and Micah get stranded on Guarma for a while and fight to survive and get out. And also Dutch decides to brutally murder a old woman, who yes did threaten Dutch with a knife because he couldn't pay her back for her leading them to a entrance to the place Javier was held at, still decided to brutally murder her in front of Arthur.
His growing dillusion of believing John may be a rat, Arthur becoming sick and Micah's growing influence on Dutch with Hosea now gone: This is honestly self explanitory.
Hope this was easy to read through and understand and I hope I did a ok job explaining what happened to Dutch.
