Depends on what your party composition would be, TBH. If you're having Eladrin and elves and dwarves, they might want naturally to find a modus vivendi that is mutually benefitting to both groups. But, in order to prompt that, you'd have to make sure that everyone was acting in good faith in the backstory leading to this (or there is a way to punish the guilty) and have Elves be unhappy with the current setup (so they have a vested interest in looking forward to returning back to the island. Same if your PCs are all hailing from the decaying port city, they'd be interested in making it thrive and therefore look for a solution to make darksteel trading resume, which isn't something that will happen without them.
Or they could try to find new trading routes and embark on a ship to explore nearby island in search of thing that would be worth trading at their port: do not underestimate what players will do, they are wildcards. I'd recommand having a (very standard, but since you're a self-avowed new DM) "session 0" where you ask the players what themes they would like to explore, in broad strokes: maybe they'll feel they want to explore the world and interact with it, and feel cramped on a desert island? It's worth knowing before you create a lot of plot points that will be prepped for nothing.
If you want to introduce the setting in episodic way, have their first task to be "gaining understanding of the situation". They live in a crummy port city, with dwarves in nearby mine. OK. They don't necessarily know what happened, and if the forest didn't disappear overnight, nobody might remember about it in the (presumably human, shorter lived than elves and dwarves) port. So, sent them on a pretty standard exploration (our live suck, we were supposed to board a sailing travelling ship, but a fire happened and its mast was destroyed... We're out of luck... let's try exploring the ruins that are supposed to hold a treasure, maybe it will change our live!" Meanwhile, use NPC interaction to make them learn that losing a merchant ship is a big deal because there is no longer any large ironwood tree to make masts and the community just lost an important asset, as their merchant fleet as been diminishing over centuries, since they could no longer build new ships and only cannibalizing others for spare parts. Have them explore their ruins and see bas-relief with a lush forest, prompting a mystery: what happened to the forest and the strange creatures depicted besides the elves (eladrin)... and where are the elves BTW? So episodically, they might go see the dwarves (have a few adventures where the background about darksteel item being rare and once produced there imparted to them) and befriend them if they are helpful enough... then they might learn about the forest of old (the elder dwarves have seen them, but most dwarves think it's just a story...) but they might not be able to cast a planeshift spell, so they should look for a ritual opening the gate in the ruins they visited in adventure one (yes, the megalithic structure was a dimensional gate, but how to open it?" Then once they are ready to cross to the other side, have a few adventure to befriend the eladrin an let them know of their problem, so in the end they can work out a solution.
BUT do not imagine how the elves and dwarves could "make peace" yourself. The players will certainly suggest TENS of ways while talking between themselves at your table. Support them. Players like to be heroes and that might be "discovering what was hidden" but sometimes it's difficult to make them find it without railroading them, so... don't have (too much of a) plan. Reward imagination and engaging with the world by having one of their solutions be "the best one" and enable it.
If you want the story to evolves from the players, implement the themes they like (discussed at session 0) to make a world interesting so they'll want to interact with it. THEN they may become a force of proposition. Some playing groups are more passive than other, so be prepared to prompt them if you feel they'll be afraid of going full sandbox, but at the same time be ready to listen to them and the solution they'd like to implement.
Maybe it will be "yeah the elves are 100% right, we must convince the dwarves to stop longing for darksteel so the forest can be brought back in its rightful pace". But they won't be able to initiate adventure before they are familiar enough with (and attached enough to) the setting. If you want to lightly prod them toward a direction, mention something you'd like them to investigate several time in different contexts. If 3 unlinked NPCs speak of the Tavern of the Drunken Dog, this is certainly a place they'll memorize and want to investigate... Being barred from something is also a great way to have players adopt the goal of overcoming the obstacle. "Only the worthy can open this door" leads invariably to "how can I prove I am worthy, o noble door" (even if it's just the janitor closet).