The fights in the game are too easy,once you have well equipped units.
Preparation period:
Here's my strategy, remain neutral with everyone, fight your way around and make an army of 50-70 whatever units you prefer,then use velvet/spice caravans from top right to go bottom left.Buy a trading contract from a mayor(That costs 45.000) and repeat several times for easy profit. Use CTRL+Space to fast forward the game on the world map.
Go to a mercenary camp of your choice,preferably the one around a faction you will want to fight for,for easier access later on.
Disband all your previous army and buy as much Cavalrymen as you can,around 70 is fine.
Start buying the best equipment(Hint:It's the most expensive one for each category) for your cavalrymen from the mercenary camp leader.Continue to make caravan travels as much as required until you bought the best.Buy both a melee and a long range weapon,but make sure the long range weapon can be used on a horseback.
Congratulations, you now have the best unit in the game,an amazing horseman that can also use his gun as well as a marksman, with excellent armor.As a bonus your party will also move very fast on the world map,because all are riding a horse.Continue with the caravans,until you make around 1 million gold and deposit it to a city with a merchant guild to gain 14% interest.
Buy 4 Large bombs and expensive hand crafted equipment,a fast horse and you are good to go.
Link for caravan trading steps:
http://www.gamefaqs.com/boards/620581-mount-and-blade-with-fire-and-sword/59030243/655296865
Additional tips to the steps above:
-Stay Neutral with everyone and make sure you have an army of 50-70men, doesn't matter what they are, to scare away bandits,thieves etc.
-Hold CTRL+SPACE to accelerate the speed on the world map,so you don't have to wait ages to make one travel.(This is not a cheat)
-Only bother yourself with Velvet and Spice and don't bother sending if the profit for each item after "Assessing Prices" is below 1100,unless there is no better alternative from a nearby city.
-Make use of the "Assess prices" 2-3 times in a row to see which city is more profitable to send to.
-Most profitable cities to start a karavan FROM: Bakhchisaray and Kafa --TO--> To Narva,Vyborg and Novgorod.
-Always carry with you 1 piece of VELVET and 1 piece of SPICE. That's all you need.If a city to start a caravan FROM, doesn't have velvet or spice, then sell it to the marketplace,go back send a caravan and go back to the marketplace immediately to take the piece back.
Combat Time:
Equip yourself with 4 large bombs or 3 large bombs and 1 melee weapon of your choice.
Ask your army to hold position at the beginning and fire at will.
If there is a hill upfront, then tell them to hold position up the hill so they can have sight of the enemies.
Charge in
on your own towards the enemy, throw bombs infront of their cavalry to hold their charge and then the rest of the bombs on a crowd of units.Once done, go back to resupply from the chest that spawns near your flag.Rinse and Repeat.
Once the enemy is weakened enough or they reach close to your troops,order them to charge and they will demolish everything.
At Castle sieges, always use the ladders option; the enemy units up there get clustered together which is ideal for the bombs area of effect.Once you run out of bombs, just look on the floor to equip yourself with a shield and a sword from the dead men so you can continue fighting.
Earn Renown the way it was meant to be-strategy-thingy:
Are you tired of farming the silly quests that give you 1 and 2 renown as a reward?
Then start doing it the fun way. First you must do the preparation period i mentioned above, then you need 4 large bombs.
Find a large group of enemy units moving together on the world map and engage them.Make sure you are fully healed before the fight.
As soon as the fight starts,tell your men to hold position and fire at will if they have guns.
Position yourself on top of the chest and hold position there.
The enemy will charge towards you,start aiming high and throwing bombs like a madman,prioritise hitting the cavalry riding infront of you.
Re-equip bombs by interacting(F) with the chest beneath you.Fire away, rinse and repeat until there are only a few men left.
Do not bother yourself with the few cavalrymen that will manage to assault your men, just focus on throwing the bombs.
In case there are a lot of long range units remaining,then you will have to charge solo and throw bombs at them while you pass near them.
Repeat until the fight ends.
Congrats you have earned 200+ Renown in a matter of minutes,without cheating.
The larger the enemy army and the difference with your own army is,the more renown you gain.
As a bonus you also get vast amounts of experience,since most kills come from you,thus helping you level faster.
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I'm using swedish cavalry mercenary this way and my casualties are very low even when I fight against ten times my army size.Difficulty is Normal on everything.Without bombs you can still do good but only against army sizes around three or four times bigger not more.