City Investment

A city has a chance of being invested by a unit with a Leadership promotion, and with a minimum of military units depending on the size of the city.
    Population 1-2: 4 units   |      6: 7      |  12+: 10
                      3-4: 5         |   7-8: 8      |
                     5: 6             |  9-11: 9     |
Affected city loses all trade routes, connections to resources, and can’t collect resources from tiles for the duration of investment.
Coastal cities require a naval blockade as well: one ship per number of water tiles adjacent to the city. (If a city is on two bodies of water (i.e. on a narrow isthmus) both bodies of water require a blockade. If the defender has flight, then an aerial blockade is required.
The chance of success of investment depends on the Leadership level: I-60%, II-80%, III-95%. The success of the investment is calculated each turn.
The investment ends when the siege ends, or can be broken by the defender attacking the sieging units and killing enough units to bring them below the minimum required to invest the city.