I believe that Lord had captured others during the road to the King. However, the question is how are you going to settle them? Let me show you the function and effects of the prison.
Meet the building ─ Prison
The Prison can be unlocked after the Village in the territory upgraded to lv.10. There is the chance to capture the hero who belongs to the other Lord by defeating them as their Lord participated in the battlefield.
There is a chance for the opponent to be your prisoner if defeats the enemy.
The Prison is not merely the place to imprison a captive but provides different BUFF based on the prisoner level.
The level of the chart is based on the castle level of the prisoner.
Lords with a castle level higher than Lv.17 can be executed. Both capture and execution can bring BUFF effect to your territory. Lord can either wait until the end of the period to execute directly or use execution order to instantly execute the prisoner. The execution order can be obtained from the Merchant Ship or special events. Increasing the execution BUFF effects according to the number of Lord you captured.