Level 10 adventuring party small army versus Level 7s with large army, who would win?

[Scalenex]

I am trying to reconcile real world medieval combat and D&D/Pathfinder combat. There limitations of money, food, and various supplies, but I'm going to guess that a smart ruler will end up garnering both PC class and NPC class soldiers, as many as he or she can reasonably afford, with the best training and equipment he/she can reasonably afford.

A 20th level anything can probably take on an almost limitless number of 1st level warriors, so I’m going to use a less extreme example.

Country A and Country B are at war. Country B is invading a border region controlled by Country A, but this border region has ethnic ties to both Country A and B, and this piece of land has changed hands a lot in the past two generations. There are sympathizers to both A and B, but most of the populace doesn’t care. Most of the civilians just want to not be hassled. For simplicity, let’s make all the participants human.

Army A
A 10th level adventuring party with a wizard, cleric, rogue, fighter, and bard are commanding a small army. One of them is technically in charge, but the army will listen to any member of said party.
The army is composed of about 500 men. 10% mounted, 30% archers, 30% hand weapon and shield infantry, and 30% polearm infantry. The average level of ability is 3rd level warriors.
There fifteen fourth level members of the army with PC clases. Five fighters of them are fighters, most of them are subcommanders for a portion of the army. For example, a fourth level fighter that took all possible archery feats leads the archers.
Five of them are rogues, rangers, or scouts. Their mainly there to be the army’s eyes.
Round it off with two clerics, a bard, and two wizards.
There are about a two hundred camp followers to perform menial labor. Mainly the cook meals, dig latrines, help set up camp, etc. They can’t fight, but if ordered to they can dig trenches and line them with sharp sticks or make simple fortifications like that. Maybe 1 in 10 have a skill directly applicable to the war effort like armor smithing or healing.
If the commanders decide the camp followers are liability 90% of them can be dismissed with the main repercussion being the soldiers are upset they have to dig their own latrines.

Army B
They have a 7th level adventuring party with the same composition: wizard, cleric, rogue, fighter, and bard. Their army is identical except they have a 1000 troops, 30 4th level PC class holders, and 400 camp followers.

Borderland C
There are about 10,000 civilians. If pushed, Borderland C can field 100 2nd level warriors (20% archers, 80% light infantry) and 2000 1st Commoners armed with spears. There are about 20 PC class holders averaging 4th level. If given a “join us or die speech” either side could drum about half the NPC class soldiers with minimum fuss.
If one of the armies begins actively oppressing the populace (including the aforementioned conscription), the PC Class holders will either join the opposing side directly or begin guerilla resistance, they can also bring any non-conscripted civilian fighter with them.

The two sides are both predominantly Lawful Neutral. The soldiers are loyal and brave, but they are not insane and do not want to die. If an enemy combatant is effortlessly mowing their men down and taking little or no damage, they will flee or surrender. The commanders also have limits, and will probably withdraw or sue for peace if two out of the five of them are killed or captured.

Both the commanding adventuring parties answer to a liege lord who would like to see a chivalrous clean war and be unhappy if their representative tarnish his good name, but they will overlook this if there is a decisive victory. Both sides have a small entourage in the camp followers whose sole job is to write letters to the lord. This includes a low level wizard who can use a one-use magical item to talk to the king in a pinch if the army commanders try to censor him.

If the defenders hold out for four months, the onset of winter forces the attackers to withdraw because their supply lines become unstainable, unless the attackers are okay with pillaging supplies from civilians.

What tactics are both sides likely to use? Who is likely to win?

Does this change substantially if you make both sides Lawful Good or both sides Lawful Evil? What about Good versus Evil?

How do the tactics and outcomes change if the two opposing sides really hate the other side, and the border dispute is mostly a pretext for settling old scores?

What if you had 15th level commanders and a 10,000 man army against 13th level commanders and a 20,000 man army?

[Tohsaka Rin]

The narrower the power gap, the more numbers matter.

Really though, in the end, it's the gr- I'm sure you don't want to hear this, but the group that has a firmer grasp on system mastery wins.

If we consider this a playerless simulation, then literal numbers win, especially if you have access to Heroes of Battle, and the massed archery rules. Being able to use formations of troops, lobbing AoE from bows is going to really devastate any formations, and the side with more bodies to soak up the damage is going to win. It becomes more lopsided when you throw magic into the equation, because there's just that many more spell slots to go around.

There's few battles of attrition a large army can't weather against a smaller force with a dozen wands of Cure Light Wounds, not unless the power gap is so vast that the smaller force is one-shotting the other side.

[Eldariel]

The access to level 5 spells is a huge, huge difference. That's where the strategic scale spells like Teleport, Lesser Planar Binding, Plane Shift, Lesser Planar Ally, etc. come up. Thus, teleport-by attacks against enemy command chain and the use of monsters like devils, nightmares, angels and such, which can be really difficult for mundane troops to deal with make a big difference. While it's not modelled by the system, I'd assume there's also command efficiency difference between the higher and lower level commanders. I think HoB addresses this to a degree?

Either way, it's hard to call. 7th level party is formidable but ultimately I find a 10th level one is likely to have a bigger impact. But if the battle is already joined, the 10th level party may be short on time to make the difference. Though 1st level Commoners are likely to have rather low morale if bad stuff happens so I'm thinking a quick shock attack might just devastate the efficiency of the larger army with relatively low losses. Ultimately I'd give the edge to the numbers in this case due to the lack of time (but if the armies were a couple of days away, things might be different). And there are lots of uncertain variables that can alter the outcome.

[Yahzi]

I am trying to reconcile real world medieval combat and D&D/Pathfinder combat.
That's probably not a good idea, but you could check out Generals of Prime (http://www.drivethrurpg.com/product/218006/Generals-of-Prime), a guide I wrote for mass combat. Unlike most other systems, it doesn't change the mechanics. You can turn 25-200 soldiers into a single creature and then your 100-man army is like a dozen NPCs. Perfectly managable to just game out the whole combat.

That said, the 10th level wizard and cleric win. A 2-1 mundane advantage is not really enough to overcome the spell-casting difference.

[Sam K]

A would likely win, at least if they have some prep time (and since they're defending, they likely do). They have access to better divinations as well as Mordekainens private sanctum (to prevent being spied on) and false vision (to misslead the enemy if they try their own scrying tactics), so they can spend a couple of days learning about the leaders of the enemy army.

Then they can teleport in and take out one or two members. Just align whatever you suspect they're weak on with what you can boost the DCs of the highest. Grab the incapacitated/dead enemy party members, then teleport out. Slightly risky with teleport, but you have scry to make sure you've studied the destination. Once you kidnap/kill one or two of the enemies, your situation is much stronger. You can use them to negotiate, or you can simply loot and burn them, and use whatever you take off of them to boost your own forces.

Higher level party also have superior logistics: plane shift lets you make sure you can get whatever you need for your specific plan (Hello Sigil/City of Brass), and you may be able to use planar binding/ally to get some extra allies when you make your teleport attack.

B will be in a better position of they can force a decisive engagement early on, before A can use their superior intelligence gathering. Essentially, it comes down to whomever can play on their strengths. A should never try to fight B in a field battle, because they will most likely lose. But it's easier for A to hunker down in a defensive position then it is for B to defend against magical hit and run attacks. Of course, B can use some of the tactics described for A through the use of scrolls, but that will eat through their WBL fairly quickly. And A still have the tools to prevent too much scrying.

I'm assuming here that the leaders of A and B essentially use the same builds and have spent their WBL in the same way. Obviously if one side is specifically built/geared to win the scenario and the other isn't, that will seriously change the balance of power.