The Three Kingdoms period, which lasted from 220 to 280 AD, was a time of intense military conflict in China. The armies during this period were quite large, often numbering in the hundreds of thousands. For example, the Battle of Red Cliffs, one of the most famous battles of this era, involved an estimated 800,000 soldiers combined from both sides.
The size of the armies varied depending on the kingdom and the specific battle. The Wei Kingdom, for instance, was known to have a standing army of around 400,000 soldiers. The Shu and Wu Kingdoms had smaller armies, but they were still substantial, with estimates ranging from 100,000 to 200,000 soldiers each.
These large armies were necessary due to the constant state of warfare and the need to defend and expand territories. The soldiers were often conscripted from the general population, and the kingdoms had to manage their resources carefully to sustain such large military forces.
In summary, the armies in the Three Kingdoms period were massive, reflecting the intense and prolonged nature of the conflicts during this time.