well, I suppose I need to go into the planes a little too then...
Avion is a planet in a plane roughly the size of our galaxy, which is in itself a part of a grouping of planes referred to later as a realm. There are several realms that make up the universe, but I'll get into that later. Each realm has a theme to its planes that are organized into a geometric shape with a plane or group of planes in the middle, called a midwelt. The Realm that Avion is in, the Material Realm is a triangle, with a triple midwelt of Avion, Avito and Avire. All three of these planes are similar, but are still very different. The interesting thing about having multiple planes in the midwelt is that they occasionally collide, letting people freely travel between them... or rather, forcibly cause their immigration into a new plane. But that will come later.
The First Age
Start:Humans begin to record history.
Summary: Several human kingdoms battle for supremacy. Humans are capable of using magic, but very few/none of them have have any knowledge of it, so there is very little/no magic. This age is somewhat based on another setting of mine called Kingdoms of Canterbury, which I will explain in more detail later.
Races: humans are the only race, think medieval times or dark ages, just trying to fight each other to become more powerful.
Adventures: one king sends you to spy on/sabotage/attack/etc. another, or find a spy/saboteur, defend attacker, or etc. from another kingdom.
End: one of three things happens: 1. a truce, and then expansion until they run into elves and dwarves. 2. one kingdom takes over then expands until they run into elves and dwarves. 3. they encounter elves and dwarves and are forced to unify against them.
The Second Age
Start: Humans encounter elves and dwarves.
Summary: For whatever reason, the humans decide that the elves and dwarves are their enemies. Be it violent tendencies, divine inspiration, or just the fear of the unknown/different. Until this point, humans thought they were alone in their world, then other races show up, and powerful beings that were made by the creator to watch over the universe (who are already goofing off). These beings introduce magic to the races, further worsening the war.
Races: Humans are comparable to renaissance times, dwarfs are close to typical dwarf "warrior miners", and elves are very druidic forest people.
Adventures: bringing supplies to the troops, attacking enemy troops, scouting enemy territory, stealing enemy magic/tech secrets.
End: The dwarves and elves find out about each other and coordinate their attacks to weaken the humans, causing them to agree to a treaty. Humans would never say that they lost.
The Third Age
Start: With their new found peace, though somewhat untrusting at first, the races begin sharing ideas and exploring their world.
Summary: Now that they are not fighting each other, the humans, elves, and dwarves begin to explore more of the world they live in. They encounter several new races, such as the friendly halflings, the intelligent ellobians, the mischievous gnomes, and the unexplainable portal cats, as well as new beasts and monsters. Some people begin to colonize new lands, while some stay in the larger populated areas to further magic and other ideas.
Races: Humans, elves, and dwarves share a great deal between their cultures, blurring the lines between them. Halflings, being friendly and inquisitive, quickly take to this sharing of ideas and even helps improve on them, and also on various types of magic. The ellobians, despite their snail bodies, begin to gain a high standing as advisers due to their high intelligence and quick understanding of how things work. Portal Cats, although they started out rough, being captured and experimented on, began being hired as watchmen in large estates and buildings, and that they caught small rodents did not hurt either. Gnomes, or "quarterlings," wasted no time in getting themselves a bad, but well deserved, reputation as trouble makers, and have thus not been welcomed into the more civilized areas, not that that completely stopped them. Humans, elves, and dwarves find that they are, in fact, capable of interbreeding, causing small numbers of human/elf, human/dwarf, and elf/dwarf individuals to appear, especially in colonized areas. Possibly a gold rush during this age as well.
Adventures: Protecting settlements from animals/monsters/mean people, settle settlement disputes, moving into unexplored territories to stake a claim during gold rush.
End: The planes in the material realm collide, sending people, beasts, and even some large pieces of land into the other realms. Overall, think colonial times.
The Fourth Age
Start: With the planar collision, the world is thrown into chaos. People disappearing, strange, new peoples showing up, the landscape changing before their eyes. Panic, fear, and confusion spread throughout Avion.
Summary: Some believed it was an invasion, others trickery by beings meant to watch over the universe, some thought it was the end product in meddling too deeply into magic's core. Until near the end of the age, nobody knew what happened, the people of Avion banded together to fight the newcomers, believing that they brought doom with them. Monster people with green or yellow skin or part animal, small flying demonic creatures, even new animals they had never seen walked among them. Many battles were fought, many people slaughtered, before a wizard who was studying a portal between the worlds got stuck in the space between them, the ether, and got a glimpse of what was going on. Thanks to this new information, campaigns of peace spread over Avion, they learned how to create their own portals between the plains and contact them. Some families were reunited, some people returned to find they had nothing left.
Races: In the confusion, all of the races lost large pieces of their culture, and when order was restored the races supported each other, merging largely into one cultural group. for a time, all races were warmongers, as long as they were the majority. Some orcs, goblins, hobgoblins, and imps were able to group together and defend themselves, the beastfolk rallied under the kobold's leadership and began to make occasional counter attacks. Humans, elves, and dwarves believed the invaders were demons, devils, and other evil things out to destroy them and acted like demons, devils, and other evil things while defending their lands.
Adventures: Attacking groups of invasive races, trying to find loved ones (for selves or hired to look for other people's), trying to make treaties (latter part of the age).
End: The people try to return to normal as best as they could, sending many back to their people's home plane. Many remained, having lived on Avion for several generations, some not even knowing their ancestors had left their plane. The planes eventually ended their collision, letting people stop worrying that they might get torn from their homes and families at any moment.
The Fifth Age
Start: The planes stop colliding, and Avion flourishes.
Summary: Thanks to the information gained during the planar collision, travel to new plains is possible, people begin to colonize these new found planes. by taping into the ether, the space between the planes, devices that allow long distance communications are built, so that people are able to communicate even between the planes.
Races: While the races still have their separate cultures, they are further blending. Of course, there are some who refuse to let go of prejudices. New mix breed races appear as well as some neones from the elemental planes.
Adventures: Colonizing adventures from the third age, but on the new planes.
End: unknown (I have not decided yet)
World Beast: Every plane has a large, indestructible beast that is connected to it, on Avion, there is the Tarrasque, a HUGE monster that likes to destroy things and take long naps. It is first encountered during the second age when he interrupts a battle by walking by. During the fourth age, the people of Avion unwittingly try to destroy their world by sending the Tarrasque to one of the other planes to attack them. Had they been successful, they would have destroyed their world by disconnecting it from its world beast, as well as possibly destroy the plane they sent it to by having too many wold beasts there. Then that would have set the other planes off center, which could destroy the whole realm. Lawl. No info yet on the other planes's world beasts.
Monsters: new monsters are added every age! More on this later!