Uninvited guests.

And where is the link to this? A Berserker as a General is strange. I played as a Demon, but never encountered this.

It was written here: here. But again, you need to check it yourself. Personally, I find it interesting to play with the suggested heroes.

CityLove, so what's the secret?

A scroll.

What difficulty level are you playing on?

The hero.

Here, the question arises for the author. Is that how it should be? Or did the script just not work? What's the point of capturing a city then?

Before destroying the demon castle, I killed a Necromancer with an army of about 30 dragons and 40 banshees, after which the army grew to 50 dragons and 70 banshees, i.e., a sharp increase in the army. The Elf had 200 dragons and 350 witches before capturing his last castle; the rest increased gradually. Thank you, though, that he didn't stay in the castle and attacked himself.
As I understand it, at the beginning of the week, a hero appears, fully preserving the army, artifacts, and experience, gathers reinforcements, and attacks you again. But there seems to be another script with a multiplier that triggers when a player is defeated. In any case, castles need to be captured. At least, it reduces the number of bosses (the main heroes of the enemy).

Is the upper one the one in the Dungeon?

You also have to cross over on a boat. There was also a shipyard below, but they didn't let me scout there.

It's not clear here. My city was also being raided, but at the same time, the enemy Generals were fighting each other.

They fight among themselves, although the winner always comes out of the battle without losses, but they don't go to each other's Dungeons, plus this moment prevents you from rushing into enemy cities yourself.

That many? Why are they from different Factions?

Bone Warriors and Ghosts. I don't know what normal numbers are, but they were the main attack stacks with vampirism applied. I didn't lose them much (only with the Necromancer 200-250 skeletons and 50-70 ghosts in total) and focused mainly on them during necromancy. For example, with two Necromancer castles, each with an Askhara, there were 973 dark energy available, which is 324 bone warriors per week from necromancy. Plus, at the end, it became even easier to accumulate through caravans from the Demon and Necromancer Dungeons.

CityLove, so you only managed to complete the game as a Necromancer?

So far, yes, but I plan to play as all of them. Except that, based on what I read, I doubt I will be able to play as an Orc due to the inability to use the city portal; it greatly helps. So far, I have no ideas, except perhaps mentoring secondary heroes so that they are responsible for defense while the main one attacks, although there is still a problem related to army losses.

Added after 2 hours 19 minutes
I'm planning to start another round of hell as a Knight. Most likely, I will build a late-game strategy using vampirism on combat griffons against three Factions, crushing the Necromancer with meat. I will simplify the start of the game with a ballista, plus a tent to reduce losses in early battles and sieges. However, I don't know if it's worth converting siege engines into something else in the late game in favor of, say, education.
Another advantage of the Knight is that he has built-in stables in his city.

The build should look like this: