As for the civil war, things could have ended differently, except Prabhakaran seemed to have been gripped by arrogance.
Though he was fighting for Tamils, paradoxically, Prabhakaran also became the big killer of Tamils. He annihilated all competing Tamil militant groups ...
... it all led to [Prabhakaran's] last apocalyptic decision to fight to the last day — and the last Tamil. Through Kumaran Pathmanathan, KP, the LTTE ‘foreign minister’, we offered to bring out all the combatants and civilians from the war zone. When KP went to finalise the deal, Prabhakaran refused. The rest is history.
Unfortunate for the Tamils how it all played out, with little intervention or pressure from other regional powers. The past violence and pogroms were already indicative of the State's intent; they didn't need a second invitation.
It's the story of most warlords / strong men types. Ultimately anything less than full obedience makes them the enemy, even (sometimes especially) the folks you are presumably fighting for.
Little intervention? Literally every world power and some of the minor ones went out of their way to support the nationalists. The United States being a major reason why it was kicked off. We eventually incorporated the Sinhalese nationalist strategies in Afghanistan.
Unfortunate for the Tamils how it all played out, with little intervention or pressure from other regional powers. The past violence and pogroms were already indicative of the State's intent; they didn't need a second invitation.