I think the Sand Snakes are far lamer in the show than they are in the books. In the books, they were total baddasses. Also, i think Doran Martell was really poorly cast; the guy in the books was fat, always tired, his feet were swollen and couldn't walk. Not at all like the one in the show.
And I kind of agree with the Sand Snakes. Dorne needed new leadership and payback for Elia+children and Oberyn.
It makes no sense Oberyn loved his brother and nephew. So let get revenge by murdering them! Remember Dorne plays the long game, and their king knew this he had his son as husband to the lannister daughter and 3rd (now 2nd after joffery) to the crown. He merely has tommen killed his son is crowned as king, dorne rules 7 kingdoms pushing the dieing lannisters out of the way. He won the game with 1 death and countless hours of manipulating. Where did the poison come from that killed Joffery... from Dorne, this is just 1 example of him manipulating the outcome. As he says in the book...
"I am not blind, nor deaf. I know that you all believe me weak, frightened, feeble. Your father knew me better. Oberyn was ever the viper. Deadly, dangerous, unpredictable. No man dared tread on him. I was the grass. Pleasant, complaisant, sweet-smelling, swaying with every breeze. Who fears to walk upon the grass? But it is the grass that hides the viper from his enemies and shelters him until he strikes. Your father and I worked more closely than you know … but now he is gone. The question is, can I trust his daughters to serve me in his place?"
This shows he uses Oberyn to do his dirty work and once he is uncovered he runs to dorne to hide under his brother. His place is not to appear strong but weak and negotiable. The sand snakes were dumb in the show and threw it to the wind and openlu declared war on Lannisters and Tyrells the 2 most powerful houses plus all the other kingdoms that want them to shrivel like the wetlands.
The king of Dorne appears weak to hide their fangs, as noone trusts them. The 7 kingdoms had thought Dorne soft after years of peace and the king wanted to keep that so Tywin wouldnt come bring them to his heel. Sand Snakes have declared war they can not afford or win, the next scene with them will be Jaime mounting their pretty little heads on pikes in their water garden.