Here is a guide to the mechanics of seizing tribute from city-states. This came up over in the Fastest Science Victory thread, and it seemed the mechanics weren't well-known, so here's a writeup of everything I know. To seize tribute from a city-state involves two factors: your military value and their resilience value. Your military factor consists of two components: Overall Military Power This ranks your military against all major civs in the game. This uses the Soldiers value from the Demographics screen. Sometimes this value does not update right away, notably upon buying a unit. This factor is +75 multiplied by your relative rank in the game. In a game with N players, this factor is 75 * (N - rank + 1) / N. If you rank first, this comes to 75 * 1/1 = 75. If you rank second in an 8-player game, you get 75 * 7/8. If you rank last in an 8-player game, you get 75 * 1/8. Military Near City-State This factor compares your nearby military strength against that of the victim city-state. All your units within a certain distance of the city-state count. It doesn't matter if the city-state can see them. It doesn't matter what terrain they are on; embarked units and ships count at full value. Air units don't count. The distance threshold varies depending on map size: Standard size or smaller: 5 tiles from the city-state center tile Large: 6 tiles Huge: 8 tiles A damaged unit incurs -5% of its strength for every 10 HP of damage it has taken. (It's not -1% per 2 HP even though that's equivalent; this appears to be truncated at increments of 10 HP damage.) I think promotions don't matter. For the city-state, add up the strength of the city itself plus the strength of all units it owns. Your military factor is determined according to the following schedule: More than 0.5x the city-state's strength: +25 1x: +50 1.5x: +75 2x: +100 2.5x or more: +125 Resilience This is a complete list of every factor that can apply to a city-state's resilience value. -110: Base Reluctance -10: Militaristic type -10: Hostile personality -20: Has Pledge of Protection (this counts only once, not once per protecting civ, and does not include yourself) -300: Gave you tribute very recently (0-10 turns ago) -40: Gave you tribute recently (11-20 turns ago) -300: Low Population (if size 3 or less, applies only to enslaving a worker) -40: Enslaving a Worker If the total of your two military components equals or exceeds the target's resilience value, the option to seize tribute becomes unlocked and you can choose it from the dialog screen. Adjustments The above formulas don't work exactly. I don't know why; my best guess is some kind of rounding error. One important case is that two Shoshone pathfinders at a total of 16 strength aren't enough to get +50 against a city-state on a hill with a starting strength value of 15. Another important case is that a single spearman at 11 strength (common when a ruin upgrades your starting warrior) usually does get +50 against a city-state at 11 strength. Practical Applications In practice, the nearby-military component breaks down like this: +25: This tier is useless, because even +75 for overall rank is not enough to overcome the -110 base reluctance. +50: This is your bread and butter. This plus the +75 is enough to seize tribute from any CS unless it has a pledge or is both hostile and militaristic. +75: This plus the +75 is guaranteed to overcome all militaristic/hostile/pledge factors and get tribute from any CS. It's also the minimum needed to get a worker, if none of those factors apply. +100: This plus the +75 gets a worker in most situations, if at least one but not all of the militaristic/hostile/pledge factors apply. +125: This plus the +75 guarantees a worker. For a worker, the victim must be at least size 4, since the -300 for low population is impossible to overcome. 11 turns is the limit for how soon you can reuse the same city-state, since the -300 for very recent tribute is also impossible to overcome. You can reuse a city-state every 11 turns if you can overcome the -40 penalty for recent tribute. This will be guaranteed with +75 overall and +125 nearby. It's possible to get a worker every 11 turns if the victim has no pledge and is not both hostile and militaristic. The ease of getting tribute varies sharply with difficulty. It's very easy on Settler where you'll easily rank first overall and the CS take forever to build any of their own units. It's very difficult on Emperor-plus where you'll rank lower and the city-states build their own military.