Because of the character limit in the posts I have had to move part 2 of my post into its own separate thread. This part will detail how to destroy a clan's advantages and how to counter them.
Now I will run through to exploit the weaknesses of every major clan so you know how to take them down.
Hattori: They start landlocked and with small territory as well as only being able to produce units that cannot use this advantage. Units that can reap these rewards take up many things
1. research, it will take a while for a hattori player to research the things needed to build these units
2. a large amount of castles is a must so in the early game hattori will not be able to use their advantages just yet
3. all units that can use hattori advantages (except for the hiding advantage which all their units benefit from) are very expensive and a hattori player will need to establish a strong economy early in the game to be able to use his/her advanced units later on
4.Since the troop upkeep is higher as the number of clans decreases and there are only two or three clans left on the campaign map the increased troop upkeep is going to catch up with them
5. In normal multiplayer battles the hattori will be able to field about 1 ashigaru unit less because of the increased unit cost (that should be a big advantage
In summary, the secret to winning hattori is to rush them. If you cannot destroy them from the start you do have one glimmer of hope left. Even though they have a ninja bonus they themselves are the most vulnerable to ninjas. Their economy holds up their whole society and is VERY fragile. getting 3 units past them to disable province buildings and with the support of a few ninjas they will simply be forced to disband a large portion of their army.
Hojo: Hojo rely on their long range weaponry and cheaper castles in order to win a war of attrition. While there is no counter for stopping them from building cheaper castles time and research are still going to hold them back and their discount shouldn't be too large. Their siege weapons might cause you worry but don't let them get to you. If you know you are going to fight Hojo take a reinforcements army with all ashigaru. Simply move this army behind them and attack with you main army. They'll be forced to turn around their siege weapons and bombard you ashigaru or they will at least have to move some troops back so you can assault their engines using something like a few ninjas. If they are attacking you then wait until their equipment is out of ammo. If they breach your walls it is not necessarily bad as they will most likely spend a large part of their money and army size on siege equipment so once you can have an even fight inside the castle you will most likely outnumber their actually close fighting troops. Just remember to stay out of the siege equipment range and you have just rendered a large part of their force useless.
Shimazu: Having superior katana as well as cheaper katana makes them great melee fighters. At least that what they want you to think. They only have bonuses to katana infantry so katana cavalry will not be any stronger than normal. They are also dangerous because of their katana heroes. The melee aspect may be very threatening and you natural reaction is ranged units right? Bad idea, katana or sword units are the best armored in the game and you will need to focus fire to take them down. Needless to say that will mean a few katana getting to your missile unit line, and we all know that could only end badly. The real solution is cavalry and katana's. You might think I'm crazy saying to take katana's to fight superior katana but katana infantry get very large charge bonuses. The basic point is to hold them down with cavalry (spear cavalry is best as they get larger charge bonuses) while your katana's come in later. Using katana or bow cavalry is a bad idea as katana troops are good at prolonged melee battles. Use cavalry that will benefit from charge bonuses and trying charging and flanking their slow troops. When your infantry is close make sure to charge a unit and hold it down with cavalry while you infantry charge. Not only is your infantry superior in unit number (because they didn't get run down by cavalry) but they also got a giant charge bonus. When all of your units are in use your charge cavalry to hold down the other part of the enemy army (as you have used a large portion of your army on cavalry they will outnumber your troops.) When you infantry is done with the first group of katana simply go on to the next and so on. Though you will likely lose all your cavalry from this strategy you will lose a minimal amount of infantry. In siege you will have to use ninja's to open the gates or siege engines to clear the lower levels of units before moving in and taking the gates so that your cavalry can attack. Remember not to get into any prolonged fights with katana units unless you have a numbers advantage.
Tokugawa: Pretty straightforward. Just don't leave them unattended and makes sure there is always a capable army at your border. Upgrading your border castles for defense is a bad idea as you have now built them stronghold which they can use as a forefront for their attack. Their ninja's are highly skilled as well so a bigger castle will only make it harder to defend all the entrances. They are very strong on the surprise attack so do not make peace with a Tokugawa player after the attack as they will likely simply attack you again. Once a Tokugawa assault runs out of steam and you have made a large enough force to assault them on an open battlefield they can easily get destroyed. Even if offered peace while a Tokugawa has only started their attack they most likely want you to think you are only seeing a portion of their army when really they are using the whole thing. The important thing is make rational decisions and make sure not to let your fear get to you and always keep them under su****ion. Never let them make a surprise war and even if you have great relationships with them keep and army or two near their borders just to make sure. The extra upkeep is worth it.
Uesugi: The key here is warrior monks. They are not quite as good at charging and fighting cavalry as spear units, nor as good at prolonged battles as katana. What makes them truly devastating is the fact that they are balanced at both. Warrior monks however take a lot of money to produce and are not very good at specific roles. They are also very lightly armored. The trick is to not use elite units that perform specific roles but instead use swarms of units with very broad roles. The warrior monks are very adaptable and elite units will have a harder time adapting to changing situations. Instead simply use swarms of units like ashigaru or weak samurai to make sure that they are just as adaptable as you, but have much less soldiers. Being Oda or somehow giving your ashigaru a morale advantage will also do you a lot of good as ashigaru break quickly while warrior monks are very persistent to stay inside combat. Another important thing to remember is their trade bonus means that trade with them will help them more than you and you could ultimately be funding your own demise. There should be a few trade nodes not too far from them to trade with china so use those instead and trade the silk with another clan.
Oda: Very devastating ashigaru as the main problem with ashigaru is their likeliness to run against more trained opponents. In fact just a good charge can send them running. The Oda make sure you do not use that strategy by forcing you to fight prolonged battles against their highly adaptable swarms of ashigaru. Hit-and-run units as well as units that can break up their army will be effective. Do not assault units near the general as breaking them will be very difficult and you will get body piled by a swarm of suicidal ashigaru. They are very lightly armored so guns will be largely effective against them. Cavalry, guns and no-dachi samurai have one thing in common, they destroy Oda ashigaru. It is also important to remember to take trebuchet's in the event of besieging a castle with a large Oda garrison. They will most likely have cramped ashigaru and the trebuchet's will slaughter their shoulder-to-shoulder troops. While not necessarily being able to destroy them you do have a large chance of destroying moral before the actual battle starts which will make them much easier to rout later on. Oda can also take advantage of having a large amount of armies in the campaign early on because ashigaru can be recruited very cheaply at any castle so if you are in the early game next to Oda make sure to defend your border until you have managed to research some better units.
Date: Date use charges and short ranged weapons such as fire bombs or guns in order to break units before they even have a chance to fight back. It is for this reason that I recommend using cavalry to charge their units before they charge you. If you can immobilize their army through cavalry you can try to break their morale yourself and give them a taste of their own medicine. Use units that can stay in prolonged combat because charging cavalry in and out will not work against them. once they are reformed and know your cavalry is there they will not hesitate to counter-charge you when you come in again. This will most likely result in your cavalry being smashed to pieces by a square, charging, date, no-dachi samurai formation. Their weakest point is their morale and their vulnerability to their own strategies.
Takeda: Countering Takeda you would most likely think of taking advanced spear units, you would be wrong. Cavalry can be effectively countered with not only spears (which I do still recommend) but also many other things. First of all is ashigaru. If you have many units you can send some of them to face directly at the cavalry and protect your other units from flanking. Second you can also use short ranged weapons such as guns or bombs. These destroy morale which is usually how you would defeat cavalry (just make sure your unit is facing the right way so that they can actually use their weapons against the cavalry!) Cover is also very important as cavalry will have difficulties fighting you. The more square you make the formation the better chance you have at fighting cavalry as their charge will make them plow into you center and there they will be trapped and have to fight a large amount of troops. If you make your units more like a line they will charge through and simply be able to charge you again. It is important to remember cavalry can be easily routed because of their small unit size so anything that generally destroys moral can be an effective anti-cavalry weapon.
Mori: Mori ships are simply superior. There is not getting around it like you can with other clans. The best thing to do would be to try to capture their ports when they least expect it (but their navy will still come back from open waters to destroy you unless your navy is superior in numbers or has better ships .) Best strategy really is to make landfall as they will most likely be focusing their economy on their navy and will not have a lot of land units built yet (because of trading they will have a strong economy so be sure to take their provinces before they can build themselves a land army.) Mori are hard to counter advantage wise but it is very simple to just go around that advantage. If you have superior resources you can still win against the Mori navy but otherwise tell their generals to get off their lazy stool and take a hike!
Chosokabe: Chosokabe advantages can be countered in a number of ways. First of all their farming advantage has a weakness, it only works for farming. As most provinces have only one money making resource disabling farming in a province will make
1. that province not produce more money than it is taking
2. the taxes of that province being raised so the people will begin revolting if there are not enough troops there
In order to counter the archer bonus it is recommended you use units that are large in number, have lots of armor or are very fast (best solution.) Some fast light cavalry or melee-able katana cavalry will keep them from shooting while some spear or naginata cavalry will be able repeatedly charge different bow units. Any monk units are highly unrecommended as a good volley will destroy a large number of them (cutting through them like ashigaru, even though they cost much more to make and upkeep.) The chokosobe also have an island advantage. The best way to negate this advantage is to either attack the north and west parts of the island (their 2 ports), attacking their north part of the island (closest to mainland and their only warhorses) or attacking the south-east part of the island (capital.)
Please note that the strategies I have listed to fight these factions is only for fighting their special advantages (Date have nothing keeping them from getting archers and Hojo can siege without using siege weapons.) Just be weary that just because you are fighting certain advantages doesn't mean an enemy clan has to use them. Make sure to have your force be able to take on army that doesn't use its advantages as well.
Thank you for reading this, now stop reading and get back to shogun 2