The name half-orc is misleading. There are cases of orcs and humans mating, but most such intercourse is barren or lethal. The common origin story for half-orcs is that they are a supernatural response to the existence of orcs. Orc breakouts appear as magically generated infections. Half-orc births are a
slower response, apparently encouraged by the High Druid in the wildlands to strengthen human tribes. It may not be true that the High Druid is responsible for half-orc origins, but half-orcs are welcome in almost all groups that recognize the High Druid's leadership
Half-orcs are most common outside the Empire in the barbaric wildlands. Until the last century or so, half-orcs were rare inside the Empire except on the frontier. But that has changed. One of the more warlike Dragon Emperors formed a unit of halforc warriors and magicians as his personal bodyguard. In the process, he gave half-orcs official citizenship in the Empire, and they’re now nearly as common as the other non-human races.
Many half-orcs don’t take to urban life but feel easily at home in Axis (the imperial city of war and gladiatorial games) and Drakkenhall (the Blue Dragon’s half-ruined city of monsters). There are half-orcs in Concord, but they don’t maintain a racial identity there, instead going with the flow of whoever their friends are.