Far from the squids and crabs and humans, an intelligent flying caudel lands on the mainland, its four avian-looking wings being the first caudel flesh to touch any land beyond the island. They are explorers, and wish to explore the new world they have found. They already have discovered fire, tools, and language, but are yet to create a farm. They are smart, and manipulate their ingenious tools using a complex hand found under a fan of tail plumes
just a quick clarification: there is a main island, as you have said, but there is a group of smaller islands that arose due to volcanos and such 
just thought I’d let you know!
The humans eventually become more sapient as the other creatures do as well. The gunner crabs and the squids are finally getting along after millions of years of contstant struggle with each other, and the arachnids are making trade with the humans.
I think we should nail down the location of the various events of the world: I propose that we say that the humans, squids, arachnids, and guncrabs are in West Africa, and the intelligent caudels are in Southeast
Asia
The Caudels, having explored the ground, have found some useful crops and have discovered agriculture as the other intelligent beings have. They have expanded outwards throughout Southeast Asia (or wherever we might decide they are), and have also reached further into East Asia and South Asia
The arachnids establish roads between many of their cities and the human’s. This helps increase the wealth of both nation, causing the arachnids to become extremely wealthy.
The squids start seeing the arachnids as a threat, and call a council to decide what to do next.
A tribe of guncrabs obtain some propeller crabs through trade with the squids. They manage to use their knowledge of firearms, and studies of the propeller crab’s anatomy, to create simple missiles. They plan to use this knowledge to try and conquer the squids
Some humans see tensions rising, and decide to travel northeast to avoid any war. They end up in the Middle East, and build many cities
The caudels expand further, entering Central Asia and the Middle East
With the humans moving and abandoning their cities, the arachnids take over the old cities. They begin constructing countermeasures for the missiles.
The guncrabs launch their missiles at the squids, who had not prepared for such an event. The squids surrendered to the guncrabs, lest they be completely wiped out
The caudels move into Eastern and Southeastern Europe. The caudels of the middle east trade their numerous unique crops with the humans, as they are peaceful creatures
Alarmed by the hostility, the arachnids launch an immediate assault on the guncrabs while also working on missiles.
The arachnids fall to the guncrab’s superior weapons, and they are unable to replicate their missiles due to lacking the insight into fire and firearms that the guncrabs had. They retreat behind their walls, but the guncrabs are still ready for war
Some coastal squid cities are also alarmed by the attacks, and create a fleet of self-sufficient sailing ships to send west and avoid the wars
The caudels of Europe travel west, and take all of Europe. They then, seeing no more places to expand to, prepare to travel north into the cold. The caudels of the middle east enter northern africa, but stay far from the conflicts between the guncrabs and squids
The arachnids and squids team up to stop the guncrab threat, with the arachnids supplying food, supplies and additional forces.
They begin to push the guncrabs back. The Caudals realize that their empire is to large, and split into two almost identical countries.
The Caudals realize that their empire is to large, and split into two almost identical countries.
The caudels weren’t supposed to be a single empire, they were many small tribes that expanded over the world due to a drive to travel
Also, the coastal squid’s fleet goes west and ends up in South america
Ok then. The squids mark down the new land, but head back and attack the guncrabs with the help of the arachnids. The guncrabs are defeated and driven back to a single city.
Some of the squids stay in South America, and create a city. They find many unique plants and animals, some of which would be quite valuable to the african squids
The guncrabs repair and reinforce the walls of their city, and work on creating more powerful cannons and missiles. They also create muskets in case their walls are breached, and place cannons on the walls as extra defence
The caudels of Europe have spread north. They have also told other tribes of their methods, which spread to Asia and allowed the caudels there to enter Siberia
The bioluminescent sharks make a return to the shallow waters as they now hunt fish.
The humans build advanced agriculture and invent a temporary writing system for themselves.
The squids make reinforce their infrastructure, and continue to make more buildings.
The gunner crabs continue to upgrade their missiles and they build more farms.
The South American squids send merchant ships to Africa, and sell their unique crops to the numerous coastal cities
The northern caudels enter North America. The african caudels have expanded south into the remaining uninhabited regions of Africa
The bioluminescent sharks expand their range, and the humans build towers to watch the weather.
The Yellowstone volcano erupts, spreading ash everywhere and reducing the day part of the day night cycle and killing plants.
The squids, humans, and arachnids form a temporary alliance so they can share their food.
The guncrabs send out their missiles, destroying many cities. They take over much of the squid’s, human’s and arachnid’s lands, and wish to expand further. The remaining arachnids, squids, and humans flee to the middle east, and join the human cities that exist there
The caudels expand into North America. They encounter the South America squids, and trade some of their unique crops to get food. The American squids send a ship to trade with the African squids, not realising that they have been conquered