Humanity
Of all the myriad intelligent species of the world, humanity is the most numerous, possessing a perfect blend of high birth rate and community focus that drastically decreases their loss rates to infighting or predation, this advantage quickly gaining them the upper hand in the eternal struggle for life. Their dominance could not be stated without their history, however - humans have always been considered somewhat third rate by other intelligent species, lacking the singular benefits of the others. Humans are not swift and gifted in mental accuity as the elves, nor are they robust in every way and quick to exploit the world as dwarves are - much of humanity has instead focussed almost solely on agricultural pursuits. Combining this with their incredibly wide band of comfortable climates, the other species were content to exploit humanity as the primary agricultural producers of the world, coming to rely on them for food for many communities. This reliance lead to their mutual protection and the facilitating of their spread throughout much of the known world - and when the Elven empire fell, and the Dwarves dug too deep in their ancient Fortresses, humanity of the time cared little. Now all other species are in their twilight, and none dominant the landscape so much as humanity, though few among it remember the reasons why. But the other species have long lives, and long memories - and the grudge remains strong even now.
The humans of the Basket are a mixed lot, spreading many thousands of miles from the northern Wastes to the Mountainholmes of the South and East. They are broken into many loose nations, each owing loyalty to one or more Great Cities, though these overlords are a distant and unknown thing to many of them. Instead, the daily masses of humanity live in their majority in small villages surrounded by farmland, no more than a dozen families between them at the very most. Such villages owe their allegiance, and their tithes, to the local Lord, who frequently resides in or near a large walled city of several thousand souls, and it is these Lords who must send their own tithes to the Great Cities in turn, under the threat of their removal from life.
While much you hear of humanity will focus on their soldiers, these are far and again in the minority of people, even amongst their own armies. To outfit and train a single dedicated soldier takes a thousand working humans, from the tailors, weavers, smiths, miners, artists, and farmers needed to support them all. Every military force comes with its own mobile city, their camp outnumbering them twice over with families, cooks, tradesmen, whores, healers, and other assorted hangers-on. In answer: the most followed profession of all is that of the subsistence farmer and the hunter, though all sufficiently sized settlements train to a degree. The world is a harsh place, with villages under constant threat of beastmen, orcs, and the followers of the Outer Gods just as much as they are of starvation.
Humans have an odd relationship with other species, as well as users of magic. They are not especially xenophobic, with the exceptions of the Great Cities, but often are fearful of other species due to the great power they hold in comparison to humans - elves are swift and silent, and are best known through the tales of dark elf raiders and pirates that slaughter villages before any have a chance to strike back; dwarves are excellent trading partners for their advanced prosthetics and their black powder, but there is always the fear that they will one day come to break open the cities they purchase from; and that is not even to mention those that seem hellbent on removing humanity from existence. Humanity's main strength is its sheer numbers and its value as labour, and they are well aware of this. And yet despite this, there are things far worse than mere fears of what the inhuman might do: sorcerors and wizards roam the lands, undead claw at the feet of isolated villagers, daemons and elementals stalk the distant night. Most ordinary people, even among the dwarves and elves, can do little about this. But non-humans are longer lived, and have comparably far greater experience in such matters - only a mage can slay a daemon, or a ghost. Those that are inherently magic have human perception tinged with fear, yes, but they are more than simply necessary to survive, they are a lifeline in a world of darkness. This goes double for those of human origin: on first contact with a mage, or even vampire, the wise human is wary, but such beings are born with nothing short of pride should they prove trustworthy. That is, until the Great Cities gear of such an agreement, and send in the soldiers to bring these wayward humans back in line, even if said line is nothing more than a mass grave.