The thing is: The game wants you to be prepared for all kinds of battles. Currently there is no battle you can’t win if you have prepared well enough.
In your post you are talking about fighters and that you had to create some right before a battle in order to win. I guess you are mainly using footmen then? This is the first mistake. Footmen are only useful for the start. They won’t survive later battles because they dont have enough defense. So promote your footmen to knight and archer as soon as possible. Your aim should be to have at least 3 knights and like 8 archer at the end of the game. And also at least 2 (better 3) clerics. Your archer are the damage dealers, your knight the damage takers and the clerics support from behind whoever needs health.
If you struggle at the start already, then I suggest you have a carpenter and a mason as soon as possible. Especially at the start it makes a HUGE difference if your footmen are equipped with a wooden shield or not and a weapon (I think it is a stone hammer) from the mason. Also try to get a cleric as soon as possible, since it takes alot of time to recover health naturally and potions can’t be used during combat. So try this:
- Right at the start, promote one hearthling to footman
- Now get a carpenter/mason and let them build a wooden shield and stone hammer asap
- Your footmen will now be significantly stronger against small critters. He can literally take on double the amount of mobs without dying
- Now promote a hearthling to herbalist and let him build dozens of potions/bandages until he is level 2. For that you need flowers/silkweed. Both ressources can easily be farmed naturally when you start in green/gras environment. Just place 10 flowers and 10 silkweed close to your base right at the start of the game. This way, you will save alot of time getting flowers/silkweed during your playtime
- Once your herbalist is lvl 2, let him build a book and promote him to cleric
You will have an easy time now, since the footmen + cleric can take on most of the waves from the start. Goblins, wolves, undead and bugs are really no problem thanks to the heal. Big Wooden Golems and Big Stone Golems are problematic though, so you should either get a second cleric or 2 more footmen. I suggest the latter, since you need highlevel footmen latzer on to promote them to knight/archers.
Once you have done the above, you should try to get a blacksmith asap. Let your mason level until he can build a blacksmith hammer and then promote the mason to blacksmith and let him craft craft craft. This way, you will easily get the knight shield and the upgrade from footmen to knight HEAVILY increases the defense of your units. When you havbe reached this stage, just promote more and more hearthlings to footmen and once lvl 3 to knights/archers.