Okay, so I'm going to start with the civs I know and I'll be asking the top players of the civs that I'm not so sure on for their thoughts, though I should be fine.
Army composition is everything in treaty and while smurfing I see too many people doing stupid compositions to counter even worse ones. So here is my guide for n00bs; when to be agressive and what to make, and when to be defensive and how to sustain economy.
I will start with the Tier 1 civs and work my way down (maybe Tier 1 civs after if I feel like it)
British - Being aggressive
The first 10 minutes of fight are some of the most crucial for British. The first few minutes your composition may vary between Muskets/Grens/Hussars with one or two mortars to Musket/Horse art/culv. Ultimately it depends on your opponents civ and their composition.
Vs melee (Germany/Spain) - You want to spend the first 2 - 4 minutes of fight with lots of musket as meatshields protecting your horse cannon and culv. This is an expensive army if you end up throwing away your cannons, so be sure to play economically. You want to be building up your FB and securing the flanks with stables so you can pressure with 5 huss if you need to. Vs Germany you want to get your Longbow card out after AA and training cards (and nat if you have them) to target the WW. Brit have the disadvantage with the natives (being food heavy) and have the advantage without the natives (better eco than german can sustain). Vs Spain you want to block lancer with hussar and have 5 - 10 goon and musk kill the lancer while musks are used as a meatshield against rods with horse art picking off rods and skirms. IF you have natives, you must be careful not to overspam and use them to block rods as well. If they have lots of skirm and not too many rods/nats (usually when their economy is low) transition to a longbow hussar composition.
Vs range (Port, Brit etc)
You want about 3 - 6 minutes on musket/hussar/gren/mort to push your opponent and keep their fb down, taking map control. Setting up flanks is essential as huss are a major part of this composition. After that 6 minute mark your opponent would usually have set up a solid position where a good skirm/goon combo can counter the close range style of musket hussar. This is when you transition to longbow. There are several rules with the longbow composition - you cannot be over aggressive as you will end up with too many lb and not enough anti cav, leaving you vulnerable to flanking cav. You MUST NOT have you lb at the front of your army - wood is scarce in treaty so you want to have muskets as the main meatshield with lb at the back. Abuse their 26 range.
British - Being defensive
Longbows/goons/art is the best defensive combination as British, making sure you cow effectively and only take ground if your opponent hands it to you. This kind of play style should be used when you have about 1500/1600 economy.
Germany - Being aggressive
Germany's weakest point in the game is at the beginning of the fight. It is important that you construct your forward base ASAP and not too close to the fight to begin with (unless you have both training cards out). Germany is best used in the Natives as their economy is very strong and can support natives the best out of any civ.
Vs melee You want to have natives out at all times with skirms and art, if they are a melee cav civ then you go skirms to pick off the inf, 3 - 6 WW microed to the cav and doppel/native as the main base of attack to tear apart their units. I cannot stress how awesome doppel are, though expensive, once the doppel cards have been sent. TIP: Send Solingen Steel ASAP with this.
Vs range One of my favourite along with Musket Huss for brit is doppel ( + nat) Ulhan skirm. Just be sure to keep 200/200 population most of the time, about 20 - 25 skirm with 10 ulhan and 15 atleast doppel. you cant do this if there is a huge field between you and your opponents army so only do this if you can get close. It is extremely effective if you have 70 - 80 vills (not too low because you will drain and not too high because you won't have enough pop).
Germany - Being defensive
Germany probably have one of the best defensive strats in treaty, alongside brit. The ability to vill up and down as their eco changes is very important to learn - you need to be able to recognise when you are draining more than your opponent. TIP: Do not go over 100 vill as SW cost 20 pop, and gives you only an 80- pop army. The composition is usually skirm with some war wagon (not too many as they are pop heavy) with culv.
Portuguese - Being aggressive
Portuguese have to be one of the simplest civs in treaty, but they are fairly solid. Their boom is above average (should be at least 2100 in most games) with pretty decent units and artillery. In order to play port effectively you must be cost efficient (expensive base unit - cassador - costing 80 food and 40 coin which is much more than a musket) and have fair map control skills.
Vs melee - Melee civs do very well vs port as port are a long ranged civ, therefore you want to keep your distance. Civs like Germany and Spain can take you in close, forcing you to make muskets as a meatshield. But do not get too musk happy as your economy cannot support it as well as other civs. 20 - 25 muskets at the front of your army as a meatshield should do with cassadores and organs bahind. One mistake with port is that people tend to make too many dragoons. REMEMBER they cost 2 pop, so do not over spam. You want to keep them at the back of your army AT ALL TIMES. Their 20 range means that they can last a fairly long time.
Vs range - This is where you want to be as Port. Your best composition is cass/goon/art. not too many goon, maybe 5 - 12, with a solid core of cass with a few organs, culv and 2 mort at most. Again keep mort at the back of your army. Make sure you secure flanks so you can wall and whore mort all over their fb. I'm not an expert on port (i find playing them boring - too easy) but that is the basics.
Portuguese - Being defensive
Basically all you need to do is skirm/goon/art. Just sit and pull back when you need to. Keep 1 - 2 mortar out at the back of your army. If they are a melee civ again you will want slightly more musket and organs, with goon to support the anti cav. 15 - 20 skirms should pick off what your micro'd organs can not.
Spain - Being aggressive
Spain are all about being aggressive - taking your opponent into melee and pushing them back as fast as possible. With an average economy you can't afford to sit and drain or make the wrong composition. There are several ways to play spain, most of them are bad. I'm going to outline the main aggressive composition.
Vs melee - Spain is itself a melee civ, so even in a mirror this will be what you want to bring your opponent into every time. You should only really need skirm, lancer, and rods - rods are for the meatshield block and vs both hand cav and ranged cav, skirm pick off the heavy/melee inf while lancer do the real damage against skirm types. 9 times out of 10 you should not lose with spain. However this is not a perfect world, and the cliff can sometimes screw you over. If you end up having to split your army you are as good as dead, so be sure to get a fast, agressive push going with a mort or two and wall your flanks.
Vs range - Basically the same. Bring them into melee, but having an additional 2 - 4 culvs out for the anti-inf cannon. If the cliff is in a bad position to be pushing and you end up draining, do not be afraid to back out a little to a slightly better position where you can drain them.
Spain - Being defensive
You do not be defensive with Spain. No good compositions.
Iroquois - Being aggressive
So first and foremost I would NOT recommend playing as iroquois in the first place as they are they hardest tr civ to master. If you can get a 2500+ boom without BB card then you may want to flick through this. Iro have a hard time against cavalry - toma are too wood heavy to mass and musket rider aren't that great. Firepit is the key the the battle, so be sure to learn the hotkeys (I haven't but that's fine b/c I make up for it another way). It is important to find the balance of when to have over pop dance (225 max population), faster training dance and attack dance.
NOTE: Iroquois should always have the natives and in the cliffs.
NOTE: Your Warchief has the 15% boost to unit hp. Put him on stand ground and at the middle - back of your army. If he dies, use your firepit to reborn him.
Vs Range - Being agressive is what iroquois are all about. After about 4 - 6 mins of being defensive and hopefully draining your opponent 100 points-ish, you want to get aggressive - you have a limited wood supply. The basic composition for this is massed skirm (around 50%) with manlets, natives and light cannon. NOTE: Do not do what I do and over spam light cannon because en masse they are impossible to micro and die to culvs! Be sure to micro your natives into their cav, and micro light cannon onto culvs/cannons. It's good to have around 8 - 10 light cannon out at a time. If you want to mix it up a bit, and they seem to be low on wood (so they aren't spamming natives) or haven't got goons (which they shouldn't anyway!), throw in 5 - 10 kanya on the flanks or go for their art - but no more, they cost 80 wood (I think) so you really cannot afford to spam them. Be sure to send your cards ASAP so you can get to your infinite 25 Cherokee and 20 infinite Huron shipments.
Vs Melee - Same thing, just no kanya and more manlet. Manlet act as a really really good meatshield, which is why tomas aren't necessary. Iro shouldn't be able to beat Spain unless the cliffs are split. Make sure your manlet are always at the front of your army (they have 10 range), it will save you a lot on replacing skirms. Since Manlet have 1100 HP (FU) and .5 RR, they don't die too quickly.
Iroquois - Being defensive
For the first few minutes of fight you want to be defensive until you can get both native posts and your team more native card out. This may be the only time where you can have small amounts of toma to defend the huge cavalry spam. Manlets are your friends <3
Before you start your push with two native posts' worth of units, be sure to send the infantry cards. They upgrade all infantry, including the natives.
EDIT: I will be doing the rest of the civs as I have more time and edit them in