Grim Reaping has been a profession for a very, very long time. For the vast majority of that time, the population we serve was relatively small - well under a billion people until around the year AD 1800 (Christian Corporeal Timescale).
However, after that point, humanity figured out how to make things more efficient, including growing their own population numbers. It took only 125 years for the population to double to two billion, and the rate only began to further increase. Two hundred years on, and there's over 8 billion of them running around, and that translates into many, many souls to haul, and a Reaper workforce that is far removed from the quaint haulage groups of millenia past.
Formal organization first began around 1925: what became GRTO was first organized in one of the historic areas for Reaping - the area comprising Greece, which has the River Styx running below it. Here, the Charonic Order of Ferrymen hammered out a unified framework for coordinating soul transport and resolving grievances with each other and with those requesting specific souls.
The resulting efficiency gains quickly attracted the attention of religious figures. The great back-and-forth began, with a growing number of specialized Reapers available and capable, but the growing and dying population constantly increased the number of souls requiring transport.
This is where certain Reapers in what was then the "Stygian" region decided to join forces, and their goals have stood as the core of GRTO to this day.
Rotations between more and less active territories
Reasonable time frames for pickup and delivery - no same-day turnarounds when you're halfway across a territory dealing with another delivery!
Better-than-six-sigma accuracy in requests - this means no more than 3 errors made in every million soul collections
Policies to lower humanity's death rate:
Diplomacy instead of war
Effective birth control and instruction
Research, research, research! Better nutrition, better medical care, and how to best access both
And many more!
Improving help for Reapers - no one says this job is easy.
This has begun to bear fruit - estimations made on the available data suggest a human population peak within the next hundred years. The load will be lightened, our brothers of bone and sisters of the scythe!
We prefer to resolve problems by advocacy and dialogue, but when confronted with something entirely egregious we have not hesitated to escalate:
Slowdowns - deliberately delaying delivery of a soul. Usually used when in conflict with requestors.
Strikes - Our most powerful tool, due to the fact that souls that are not properly transported from the deceased in time will begin to "wander". Wandering souls may do two things:
If they contact a piece of equipment or machinery, they may inhabit it, causing issues for other humans
If they contact another human directly, the wandering soul may induce an intact soul to leave, multiplying the problem. A Local 13 soul-collection strike during the AD 1980s (Christian Corporeal Timescale) is thought to have caused this problem, leading to years of souless music and art at the hands of the newly soulless "Yuppies".