In all cases, if 75 + (random 0-74) < province unrest, the action fails and you get the unrest too high message.

In all cases, if 5 + (random 0-14) > province population / 10, the action fails and you get the pop too low message.

For slavers only:

• Number of slaves is exploding d6 + 4 + [invisible slaver bonus]
• if 10 + (random 0-29) > province population / 10, you get half as many
• Population loss is 10 * floor((num slaves + 4) / 5)
• Unrest is then just 1 per slave found

Lord over heathen tribes is considerably more complicated and is quite different