Complete Noob's Observation

I am not a big fan of Mix/Max-ing, which is probably why I suck at games. But RTW2 so far has seem to hide a lot of its complexity very well and as the result, seem to be a much more simpler game from mechanics point of view.

For Example, by removing population effect on taxation (our main income), and changing tax amount from buildings alone (plus your one off faction capital bonus), we can simply calculate payback time for any investment.

When starting my game at normal difficulty, I started with 5,000 wealth. So I have limited amount to invest. Is putting 1900 on level 2 settlement better or worse than putting 1600 on level 2 logging camp? All I need to do is find the "Wealth bonus" sentence on the description, count how much higher it is compared to my current building:

• Level 2 settlement: 100 Wealth bonus, Level 1 settlement: 50 wealth bonus; so net = +50 wealth per turn, i.e. 38 turns before payback
  
• Level 2 logging camp: 60 wealth bonus, level 1 logging camp: 40 wealth bonus, so net = +20 wealth per turn, i.e. 80 turns before payback

So while logging camp is "cheaper" by 300 , it is actually a lot more expensive in term of payback time.

While this is a very simple understanding , most buildings are simple enough that the above calculation is easy (they only have either +wealth, + food, + public order, +% wealth etc.). Logging camp actually also produces (80-40 = 40 more) timber, which, if I can sell them all (enough trade routes) worth 5 each, 40 x 5 = 200 income, making payback period , at best 7+ turns only (1600/(200+20)). But the problem is getting required trade routes to dump that many goods. (1 trade route = around 15 goods)

Concept of City versus Province

"There is no such thing as Cities. There are individual men and women, and there are Provinces" - Margaret Thatcher, RTW2 style

When thinking of RTW2, it is easier to remove the concept of a "City". In RTW2, a city shared the same attributes of the Province. So it is practically just a bundle of buildings in ETW.

• Public Order is shared. So if the province is "safe", the city can be ♥♥♥♥♥♥♥♥ as far as the game concerned, they are still paradise.
  
• Population Surplus is shared. So you can open an extra building slot on a city, just by milking the province's growth.
  
• Military recruitment pool is shared. So don't recruit with multiple generals in the same province, even when you are in different cities. It is confusing, but it pays to remember which cities are part of different provinces, which cities are part of the same province.
  
• Building bonuses are mostly province wide. So +% on X, will mean +% on X for all buildings in all cities in the same province. Mustering Field mean you can recruit the new unit even when they are in different location, as long as they are within province borders.

In ROME, we tax BUILDING, not PEOPLE

"Buildings are people too" - Mitt Romney, RTW2 style.

• Contrary to popular belief, "Tax" income in RTW2 seems to be INDEPENDENT of population size.
  
• In fact, I can't find reference to any population size in the game. You get population surplus (which is just a currency to open up new slot on your city), but no track of Total Population / Current Population
  
• Instead, "Tax" comes from "Province Wealth" + modifier. Province Wealth is just the sum of all cities wealth, and City Wealth comes from BUILDINGS, not POPULATION.
  
• Capital City of your Faction seems to have large bonus unaccounted by existence of buildings (at normal difficulty, Seleucid started with around 2,000 wealth bonus, while Parthia started with around 1,000 wealth bonus). This is not repeated on any other capital cities on other provinces

Tax Slider Modifier

• Base Wealth: Let say for example you have a province with 1 city. Because it is the capital of your faction, it gives you 2,000 wealth. Plus you have 3 buildings on it, giving total 300 wealth. Your Province Wealth is 2,000 (faction capital bonus) + 300 (building bonus) = 2,300 wealth.
  
• Tax Slider If you set Tax = 0%, you still get 2,300 wealth. If you set tax = 10%, you get 2,300 + 10% = 2,300 + 230 = 2530. If you set tax = -100%, then it is zero income.(not sure if you can - tested, the lowest you can go is negative 16%).
  
• Corruption Modifier: Then you have "Corruption" modifier. Say you have corruption of 7%, and tax of 10%, then your modifier is just 3%. 2,300 + 3% = 2,369 (103% of Province Wealth) instead of 2,530 (110% of Province Wealth). This is so far seems to be independent (probably building or generals can reduce this, but no active way to affect this, corruption just happens)
  
• Slave Modifier : Slaves are just like tax. So if you have slave modifier of 10%, it's the same as if you have a tax slider rate of 10%. Slaves is an active side effect of your behaviour. If you loot / raze a lot of cities, then you will have a lot of slaves. This gives you extra % of your Province wealth as income, but also reduces your Public Order.
  
• Apparently slaves die off very quickly, so if you stop razing / looting, then your slaves will eventually naturally disappear. Some buildings can slow down the rate of slaves dying.
  
• Controlling a whole province (all cities on the province) allows you to issue "Edict" which acts like an extra building (same bonuses). Losing one of the cities in the province cancel the edict.
  
• Edicts are also limited by your faction size, just like the maximum number of generals you can control increase / reduce as you gain/lose cities, there is a cap of number of edicts you can enact.

"Taxation is Slavery" - Robert Nozick, American Philosopher

More on Slaves and Corruption

• According to the tooltip, Corruption is designed to be a "soft cap" on empire size. The larger your empire / kingdom, the more corruption you will have, reducing your tax income.
  
• Currently testing the difference of Occupy/Loot/Raze on Slave population and Public Order, Slave Decline rate
  
• Slave Decline Rate: around 5% of the total slave population per turn. You can see your slave population in a province by clicking income breakdown tab for the province (NOT the income breakdown tab for the whole faction/empire/kingdom).
  
• Slave Tax Modifier Rate: around 66.67% (2/3) of the slave population. e.g. Pontus starts with 1 province, it has 7.4% slave population, after 1 turn, it drops to 7.1% (5% drop, 95/100 x 7.4 = 7.1). The tax rate modifier dropped from 5.0% (2/3 x 7.4) to 4.8% (2/3 x 7.1)

The Test below is conducted in response to the following comment:
CommodusIV 9 Dec @ 1:11pm
Slaves have a negligable presence, if any, when you raze a city. I personally find that to be better than occupying since you get the initial PO loss on top of 20 public order per turn counting down to 0 with occupy, vs an one time deal of 40 PO loss and a countdown from 5 when razing.

Occupy (Wall Street), Loot (Dungeons), Raze (Your Momma's house)

* The funny thing is the way Slavery is calculated during Occupation. When taking a city, you can see the new city's slave level on the top left icon on the box where you choose "Loot, Raze, occupy".

My province before taking the city has 3.8% slave rate. The new city has 2.8% slave rate. The new province slave rate = 3.8% +2.8% = 5.6% rate. This is mind boggling as it defies any law of mathematics! You can't mathematically adds 2 average of 2 different cities in the same province and then get the new province average.

The other interesting thing is that if you are really concerned about effect of public order to slavery (too much slave already), you can just raze the city and get no slave (they are all dead!)

Razing is also very efficient on 1 building city as the last building is normally indestructible, so you don't lose it. While on 3 buildings city, it costs more to rebuilt the lost building(s) compared to just loot or occupy it.

Public Order

• Public Order seems to be shared by all cities under your control in the same province. So if I get +20 unit Public Order bonus from having one of my city with 20 units general in it, the whole province stabilize.
  
• Opening a new field (requires Population Surplus), but not building anything on it, will turn the new open slot into slum with -7 public order penalty until it gets cleared.
  
• Public order accumulates like some kind of "Goodwill bank", so having a 20 units camp inside a city for 5 turns give 5x20 = additional 100 public order that you won't get if you camp your army just outside the city, which remains in the bank when the army leaves (of course the +20 bonus disappear, but the accumulated order from the past remain).
  
• "Military Presence" Public Order bonus seems to diminish once you hit positive number. At negative public order, it seems 1 unit = +1 public order per turn, so 20 unit = +20 public order. At positive public order, 20 unit = +9 public order only.This is reasonable: If your city is on verge of revolting, military stop it. If your city is happy, military does not make it much happier.
  
• Public Order can't go higher than +100. I was told that "Happier people pay more tax", but I don't have any data to prove or disprove that. I think it is only another myth or probably it is only on older patches?

Population Surplus

• Population growth seems to be shared on the province level, not on city by city basis. Accumulated population growth turn into population surplus, which only use as far as I can see, is to open new slot on your city (normally city has 4 possible slots, but only 1 or 2 open; unless it is capital, then it has 6 slots, around 3 open).
  
• Population growth from food surplus is shared on all provinces (+5 growth on all provinces, if you have around +20 food surplus on your whole "kingdom")

Research

• Like everything else in RTW2, research is simplified compared to previous games. You no longer need to build "School" or "University" to conduct a research. Just click on research button, pick your target from 3 military trees and 3 civil trees, and let it rip. Does not seem to cost anything other than your patience.

Spies

• Generals cannot kill spies, even when they are "detected" (visible on the campaign map).
  
• There is this idea to get the best out of trade income by either sending spies or a single admiral on a single ship all over the world just to enable the diplomacy option (you can't negotiate with faction you haven't discovered on the map yet).
  
• In war, I prefer to use my spies as "scout" , put it on the pathway between my enemy's region and mine. Since army moves really slowly, having my army out of position can cost me a lot of cities, thus I need to know where the bulk of enemy's army is at all times.

Unit Recruitments

• Each Province has shared "recruitment speed"; normally around 3 units per turn. Therefore having multiple generals recruiting on the same province means slower recruitment overall (i.e. 2nd general won't have their 1st solder until the 1st general finished getting his units)
  
• Multiple mustering fields ("Barracks") does not assist in increasing the recruitment speed. It only unlock certain units to be produced IN THE PROVINCE where the "Barrack" is built. So there is absolutely no reason to build multiple "barracks" of the same type in the same province.. You can build one infantry barrack and one cavalry barrack and one siege barrack on different cities on the same province and increase the option of units though.
  
• Recruitment does not seem to affect city or province growth.
  
• A recruiting general cannot move, so putting him inside (garrison) a city has the side bonus to "public order" (up to +20 for 20 units built in a city, I can't seem to put 2 generals in the same city, it only open unit transfer screen).
  
• Even when I don't fully control the province (only 1 city in the province is under my control), I still get the max recruitment speed for that province.
  
• Thus the fastest recruitment is possible by having 1 general per province, in the PROVINCE with "barracks" building (mustering fields etc) to get best possible unit with your current technology, recruiting max number per turn (around 3).
  
• So if I have 3 provinces (with say around 6 cities), putting 3 general in 3 separate Provinces with mustering field allow me recruiting 3x3 = 9 units per turn.
  
• Note that you don't have to be inside a city to recruit the more advanced unit that Mustering Fields give you, you can be anywhere in the province. It is just that if your army is also in a city, you get +Public Order bonus while mustering.

Army Movement

• Every army has circle of control around it, which stops enemy army from entering it, unless the enemy army has enough movement to attack on that turn.
  
• Moving through desert caused attrition damage to your army (OUCH!). Use the road when moving through desert provinces.

Basic Rock, Paper, Scissor

• Cavalry beat Range Missile
  
• Spearmen beat Cavalry
  
• Range Missile beat Spearmen

Most useful tip I read

Read this on Reddit and it help me won a single battle in one try after 4 hours trying without success (thanks to the original poster):

Right, combat 101.
Total War games are based heavily around morale, and the key to morale is flanking. When units fight face to face, it takes forever and both units get the ♥♥♥♥ beat out of them, then finally one wins and the other runs away, but really nobody gets a good deal.

However, if you attack a unit that's fighting face to face in the back, you'll cripple its morale and make it flee much, much faster.

The fundamental tactic in TW is hammer and anvil. You have heavily armoured, defensive troops fighting face to face with your opponent's troops, then you use rapid cavalry to circle behind his lines (you may need to kill his cav to do this), and charging into the backs of his men. Doing this will break them almost instantly, and practically guarantee your victory.

Moving in Formation
In Empire Total War there is this very useful command to move units forward in the same formation as they are currently in. In RTW2, this command is hidden as keyboard hotkeys:

• UP ARROW : move unit forward in formation
  
• DOWN ARROW: move unit backward in formation
  
• CTRL + Up : Increase Rank ("Thicker" unit group)
  
• CTRL + Down: Increase File ("Wider" unit group)

Not tested:

• CTRL + RIGHT KEY : Attack Move?

Tested to be NOT working (RTW2 should really learn from SC2):

• Shift + Left Click : DOES NOT QUEUE order (unlike almost every RTS out there)
  
• Double click when selecting a unit: DOES NOT SELECT UNIT OF THE SAME TYPE (so if you want to make sure all your pikemen use their special Phalanx formation, you have to select them one by one or group them only with pikemen of the same type!)