That map seems bloody impossible, even doing all I can to get the hold of resource generators and build up as fast as possible, using the elves starting bonus, and building marketplaces in all four cities ASAP, eventually the computer comes to me with grouped together units from (I guess) all his cities, and with mine being each a different type, I just can't have an army to defeat that, even if I manage to build them all up fast enough.

I know it's not (impossible), because I've beaten it in the past, but it was so long ago, that I don't remember how.

I've checked the walkthroughs on the Internet, but for me they all can be summed up as "Build up your cities and armies impossibly fast and then defeat the computer." - for Cthulhu Under the Sea's Unholy Tentacles, if I could do that, I wouldn't need a damn walkthrough!

Help?

I haven't played this one yet, so this is just brainstorming with you, rather than useful advice. :-)

If you have cities with different kinds of units, then you'll always be weaker in units than the opposing team late in the game, which to me means that you only have two possible strategies:

1. Build up a hero with great magic so that you can use spells -- not units -- to either kill or weaken the enemy units. With advanced enough magic, you can get "Curse" to apply to every unit in the enemy army, and Fireball or Meteor Shower can take out several groups of units.

2. Attack enemy cities early in the game and take them over, so the computer CAN'T come to you with four cities' worth of units.

Good luck!

United Front is one of my favorite campaign missions, so I might be able to help. First of all, please detail your strategy during the opening month (which towns you prioritize, how many heroes you're using, etc). Also, around what week or month does this powerful AI hero attack you?

Having some heroes gathering troops from various sites and hero chains is very important in this mission.

I have seven heroes from the previous mission + one randomly generated in this one.

The necromancer hero (the one I had to escort in the previous one) comes with Advanced (or Expert? I don't remember right now) Wisdom, Basic Earth Magic, and Town Portal spell in his book, so I give him the 35 elves, put his undead troops in the city (so that they don't destroy the elves' morale) and go off to fight the zombies guarding resource generators to get resources and XP to get his Earth Magic to expert (so that he can become a guardian hero, porting all over the place to chase off/fight the invading enemy heroes).

All the other heroes with their starting units are used to pick the unguarded resources on the map (Though I've just thought to use the spellcaster ones to fight the zombies as well, maybe get the resources a bit faster - I've already restarted the scenario, so I'm going to try that).

City-wise, I prioritised the Castle, as well as aiming to build a Treasury in the Rampart (to get the extra 10% gold every week). Second in order was the Necropolis (at least partially because one ofthe walkthroughs suggested it, but also because I thought to give its troops to the Necromancer hero, once it's fully built up and he has Expert Earth Magic - so that he could use them to defend my cities, and keep adding skeletons to the army without destroying its morale - btw, please remind me, if Necromancy can raise the upgraded version of skeletons? It's been a while since I played, and I can't remember - the hero had the elves first, and then Castle troops later, so I didn't get to check it).

I also wasn't upgrading the Castle units generators for quite a long time, instead using a nearby fort to upgrade the units every week (with one of spare heroes, once there wasn't any unguarded stuff to gather left - the necromancer was able to teleport in, grab the units, and go on his merry way at that point).

First priority however, in all four cities, was to build the Marketplace to handle the resources shortage (and then its upgraded version, when possible, to generate some more, especially in Castle and Necropolis, since Wood and Ore seem to be the two most needed)

Rampart got built up third (I didn't as much plan for it, as it sort of just happened, due to resource availability) and the Wizard city (Tower?) the last.

As for the powerful enemy hero paying me a visit, it was at some point in month two I think. Can't tell for sure, since I already restarted the scenario and overwrote the save. Earlier than that one, weaker heroes were visiting, but I was able to handle those fairly easily. The powerful one, I mainly remember him having at least 60 upgraded vampires, and a mountain of skeletons and zombies, plus quite a lot of the undead cavalry, too (can't recall their name at the moment). Some skeletal dragons, too, but it was the large numbers of those lower tier units that were the main problem (I had archangels at that point, who were able to handle the dragons, but not enough of them to beat everything, only 7 or so I think).

I'm thinking to, in this new attempt, try building up the three cities other than Necropolis (non-upgraded versions, so that the units start being generated, first) and try building a mixed army of higher tier units. That worked for me in "Tunnels and Troglodytes" map pretty well (also with the teleporting hero).
Necropolis will be excluded for morale reasons.
(and if I'd manage to get Earth Magic on non-Necromancer hero, who already has the Town Portal in their spellbook from the previous map, that'd be all the better, but since that's essentially random, I won't hold my breath)

I have to leave the house in a few minutes, so I'll just make this quick. As you suggested, try building up one or two might heroes since their Attack and Defense will help you survive. There's no guarantee that they'll get Earth Magic, but try your best anyway. Spend the first few weeks clearing out as much of your side of the map as possible, using your multitude of heroes to their maximum advantage. You can be somewhat flexible as far as towns go, but you're wise to downplay Tower at the start. It's been two years since I played that mission, but my building strategy for multiple towns is to use my best judgment based on the types of starting resources available to me. For example, if I doubt I can afford a Mausoleum, I'll aim for a Monastery instead. You seem to be thinking like this already, which is good. Don't be afraid to restart and try again if you need more practice. You'll find it getting easier when you become more and more familiar with the map layout.

If you do restart, restarting from the last save of the previous level gives you a different random seed. Might be better.

Yes, but only if you have Skeleton Warriors already in your army and you have no free slots in which to raise regular Skeletons. If you have Skeletons, or if you have a free slot, you get Skeletons.Black Knights or Dread Knights, depending on whether they are upgraded.

In addition to this, remember that only 2/3 of the dead are raised as Skeleton Warriors.

Some things to consider:

-If you're going to use your necromancer as your main hero for fighting the enemy, then keep a slot open to raise the dead as skeletons. As Tier 1 creatures, they are free to upgrade at the hill fort, and as lanipcga said, if you raise them directly as skeleton warriors, then you get fewer of them.

-Using the hill fort as your method of upgrading your creatures is an excellent idea, as long as you have a spare hero to handle it. Upgrades at a hill fort are cheaper than upgrading in town, and you'll also save money on buying the upgraded building.

-Likewise, definitely get that Expert Earth Magic.

-Try to teach one of your heroes (not the strongest one, that you plan to use for most combat when possible) at least Advanced Wisdom (to learn 4th level spells) and Expert Scholar (to trade 4th level spells). You'll be able to teach all of your heroes any of the spells (up to 4th level) that any of your heroes have learned. I started doing this in the Chronicles campaigns, and it has been a major quality-of-life improvement (granted, there are more maps to those campaigns). Suddenly all of your heroes can start using Town Portal once they've got Advanced Wisdom, or any of the other spells up to their relevant level of Wisdom. You can't trade Level 5 spells, but that shouldn't be necessary anyway.

-If your army is primarily undead, then feel free to add a few stacks of the stronger creatures from your other castles, especially if you have empty slots available. Even if they end up missing turns, they'll be able to provide some extra power that you wouldn't otherwise have. Look around for morale boosting sites on the map to make up for the penalty for a battle (ex. Temples). Archangels are a great creature to mix into any army, since they are powerful and they bring a +1 morale bonus. Look for morale boosting artifacts as well; those are typically pretty cheap even if you have to buy them.

-If you have a decently powerful Knight, then use that as your main hero. Stick him on the front line to do the heavy fighting and let the Necromancer continue to portal around and round up reinforcements. The Knight comes with Leadership, which lets you mix the best creatures from each of your different towns without many morale problems.

-After a quick look at the map online, with the Grand Elves starter and a decent caster hero, you might be able to hit at least one of the enemy necromancer towns absurdly early. You might possibly even be able to take two of them, which should guarantee your ultimate victory. Load up your strongest hero with everything available to him at the start of the map and send him off to level up in enemy territory instead of in your territory.

-Don't be afraid to throw multiple armies at an overwhelming enemy. The main focus of your first attacks is not to win, but to inflict maximum losses on the key enemy strengths. If your enemy's biggest strength is spells, then have your creatures defend in corners so the enemy spends more turns using spell points (take along a few stacks of Pegasi and especially Wraiths for extra spell point damage). If liches are the biggest threat, then suicide your guys into the liches to kill them. If Dread Knights are the problem, then wipe out all the supporting stacks so your creatures can gang up on the Dread Knights while suffering fewer retaliations.

After you've softened up the enemy (including having them use their spell points on your first attack waves), you can follow up and hopefully finish the enemy off. Just make sure your heroes retreat so you can re-buy them.

You've got 4 different town types, so do some mixing and matching of the best creatures from each, especially if you have some things to offset morale (Leadership, artifacts, Expert Mirth or Prayer, or just hitting some morale sites before major battles).

Creature stacks to consider:
Marksmen (shooter)
Zealots (shooter, no melee penalty)
Crusaders (okay cannon fodder to protect your shooters)
Cavaliers (durable, fast)
Arch Angels (everything about them is awesome)

Grand Elves (shooter)
Pegasi (very fast flyer, can finish off weakened stacks or be fodder if necessary)
Unicorns (durable, fast cannon fodder)

Gremlins, especially if a lot of them are available (shooter, can be replaced by stronger units when available)
Magi (shooter, makes spells cost less)
Titans (durable shooter, no melee penalty)

Dread Knights (very durable, fast, cannon fodder)
Vampires, if you have a lot of them (no retaliation)
Skeletons (only if you are using the Necromancer as your primary combat hero)

==========

You're facing primarily undead. They only have one shooter, so they'll be eating a lot of retaliation attacks. Expert Slow will be very effective on them, keeping the skeletons and zombies out for a long time. The biggest threat is probably any decently sized stack of Black/Dread Knights, then (in no particular order) large stacks of Vampires, Liches, and Bone Dragons.

My suggested creature list is heavy on shooters to take advantage of the melee nature of the enemy. Use a few melee fodder stacks to keep the enemy busy in the middle of the map while your shooters tear them apart. If the AI stack can't reach your shooters, but they can reach your melee, then they generally will try to hit the melee instead of wandering off to cause trouble elsewhere on a later combat turn.

Marksmen and Grand Elves both shoot twice, so they are great in large numbers. They die quickly if engaged, though; if their numbers get too small, then swap them out. Magi and Zealots are both solid shooters, and both bring decent backup abilities (lower spell point usage, no melee penalty).

Your liches and vampires can't use some of their nicer features (AOE ranged damage, life stealing), so neither unit is as attractive as normal. Liches probably aren't worth the effort if you use any living troops, but the Vampire's No Retaliation can still be useful if there are enough Vampires.

Pikemen and Centaurs can work as early fodder, but should be replaced by stronger units as they become available. Dwarves and Dendroids are typically too slow to work as good offensive fodder; Haste or Teleport can make them worth taking while you accumulate more of the better creatuers for later use. Zombies are in the same boat as Dwarves and Dendroids: a too slow tank that is the perfect candidate to do the dying for you if you can arrange it.

Genies are fast, but they are a little bit squishy for fodder; Master Genies can spend their first turn giving one of your guys a random buff. Naga Queens are decent, between high hp, reliable damage, and No Retaliation, but you can probably pick up Giants right after you can get Naga, and a Hill Fort means you can have Titans without paying for the hideously expensive Cloud Temple upgrade.

Pegasi are exceptionally fast, but they are also pretty squishy. They are a good addition if you have something expendable (like Crusaders) to soak the retaliation before attacking with the Pegasi. I wouldn't add them to your army as your only Rampart creature unless you have morale to spare. They'll serve a very similar role to Genies.

Skeletons may be a useful addition if and only if you're using the Necromancy skill to add to their numbers. If so, then they aren't really cannon fodder.

If you are going to splash only one undead unit in your army, then Dread Knights are the best choice (unless you have a lot of Ghost Dragons). They are fast, strong, durable, and their special abilities still work on the undead. The human Paladins can serve a similar role.

Town build suggestions:
-I suggest working on economy in the first week (City Hall in each town). Tavern -> Town Hall -> Marketplace -> Mage Guild -> Blacksmith -> City Hall -> Creature Generators, skipping anything in that chain that is already built. With 4 towns, you're going to need the income to continue building everywhere. Lanipcga has convinced me that taking gold from treasure chests is the better option, too.

-Skip the Resource Silos (marketplace upgrades) unless you find yourself unable to keep building up your towns because of a lack of wood and ore. Silos are expensive.

-Don't bother with the Treasury; it is expensive, it requires the Dwarf horde building, and you shouldn't have enough gold left in your treasury at the end of each week to make it worthwhile. You need to earn interest on 50,000 gold just to break even on the gold cost of the Treasury itself. Your resource needs are varied enough that the Mystic Pond might be an okay buy if you do it in the first week (Lanipcga will probably disagree with me about the mystic pond :) ).

For generators:
-First priority is on the Castle creature generators, all the way up to Archangels (skipping Griffins and maybe skip the cavaliers, since they are optional). Pretty much everything in this chain can be a useful addition to your army.

-Build the Rampart up to Elves, and maybe Pegasi. If you do get the Pegasi, then get Unicorns as well if you don't need the Dendroid building to do it (I don't remember whether you do).

-The Wizard town can build up to the Mage Tower, if you have the resources for it. Definitely get the Gremlin building, if you don't start with it. If you find you have plenty of extra resources, then get the Cloud Temple.

-The Necromancer can be built up as you have spare resources, if you use the Necromancer as your defensive hero. Otherwise, it is pretty much last priority; the lower tier undead don't bring anything special to the table to compensate for the extra morale cost of using them in your army. Push for the Mansion and the Hall of Darkness when you have some breathing room in resources. Make sure to get the Necromany Amplifier early if your necromancer will be doing much fighting.

-Fill in extra generators in each town after you have the important ones and you've got a few combat-capable armies on the field.

Thanks for all the replies. :)

What seems to have worked (I haven't beaten the map yet, but seem to be making good progress) is:
(I'm sharing it in case someone else needs help with this map - obviously, some of it repeats the advice from your posts, but here it's all in one place)

1) Build marketplaces in all four cities on day one (I needed to do some trading of resources for that already, but managed - important: only trade as much as you need to buy one more, because of more marketplaces giving better prices).

2) Used the necromancer hero (who in my case started next to the Rampart city) to grab the elves (starting bonus) and give them to a nearby cleric hero. Use that cleric to clear stacks of zombies and grab resource generators, heading to the north and the computer controlled areas.

3) Use all the spellcaster heroes from the previous map to fight other zombie stacks and grab resource generators.

4) Build up the Castle, Rampart and Tower as resources allow - starting with money generators and upgraded Marketplace for resources (Marketplace first in Castle and I think Necropolis, since Wood and Ore seem to be the most important two).
Unit-generators wise, in Castle, aim at monks, cavalry, and angels; in Rampart, unicorns; in Tower, giants, mages and nagas - only the basic buildings at first, so that they start generate as many units as possible. Use the Hill Fort for upgrades, or just don't upgrade the units yet.

5) Whichever spellcaster gets Earth Magic skill (if you don't have one with it yet), and has the Town Portal spell (if you were able to get it in the previous map), should be given the starting elves, and try to get Earth Magic to Advanced or Expert ASAP (so that they can use the spell to portal to any of your cities).

6) As resources allow and/or is needed, upgrade the creature buildings (starting with Rampart, then Tower, and Castle last - because of the distance to Hill Fort, Castle is closest to it), and build an army composed of, in random order:
Archangels, Titans, Naga Queens, War Unicorns, Archmages, Zealots, and upgraded cavalry from Castle (I can't recall the name of that unit at the moment). Archangels will take care of morale penalty (since they give +1 to the whole army), although having Leadership hero skill and/or morale-boosting artifacts will also help.

7) Defend your areas, until you think you have a large enough army to assault the computer, or destroy their armies as they attack you (remember: if their hero escapes, their army is lost as well).

8) Go forth and destroy them, possibly teleporting back to any city if you need to kill a pesky enemy hero heading that way, and the city doesn't have enough defenses on its own. Using the Town Portal spell, you can easily hop around every week to collect reinforcements, although in the northern parts of the map you might have to ride off the cursed ground first (it's possible to portal -to- it however, if you need to defend one of the Necropolis cities).

9) Keep building up all cities (Necropolis included at this point) as resources allow, so that, hopefully, they can defend themselves on their own, if need be.

By the time I went north with the army, the computer built up its cities too (the two I took so far, at least), so I was able to start buying armies to defend them as soon as new week rolled around.

Oh, I also parked the heroes with nothing to do in sanctuaries to act as observers - they had no armies to do anything, but allowed me to know when & where the computer tried to invade. One of them was parked in the sanctuary in enemy territory, able to ride to nearby mine and back in one day, taking it every time the computer took it back, not only giving me some resources, but also acting as a decent distraction, with computer hero having to go back and retake the mine.