Who is leading the army?

[Renzi]

I started a war and invite my two allys who send their army. They combine their army which was now bigger than my one. So I was not surprised i could not attache that army to my one, I just could follow them. I decided to buy some mercs to get a bigger army than my allies, so we could start sieging the war goals and not random provinces, but even after having the bigger army I just have been able to follow them, but Iam not able to lead.
So I will lose this war.

tldr: When are you able to attach an army and lead it and when are you just able to follow them?

 

[Knotz]

You can't control allied armies.

 

[Tatterhood]

You can't control allied armies.

Sometimes they decide to follow you around, though. I'm also not sure exactly what is involved in the AI's decision to do or not do that.

 

[covya]

I started a war and invite my two allys who send their army. They combine their army which was now bigger than my one. So I was not surprised i could not attache that army to my one, I just could follow them. I decided to buy some mercs to get a bigger army than my allies, so we could start sieging the war goals and not random provinces, but even after having the bigger army I just have been able to follow them, but Iam not able to lead.
So I will lose this war.

tldr: When are you able to attach an army and lead it and when are you just able to follow them?

sometimes the AI allies will choose to attach to you. that's the only time you'll be able to exert any control over them. not actually sure how the AI decides whether or not to attach.

 

[Renzi]

So it is normal that they ignore the wargoal and that I need 20 more men to siege it... and I can not do anything to change that?

 

[Renzi]

Iam also kind of sure that I did that in the past, I was sure the the size of the army was the key and really surprised it did not work

 

[ragnarok246]

not actually sure how the AI decides whether or not to attach.

It's quite simple. If the AI is allied with another AI and it has a war that the player is an enemy in, even if not called into that war, it attaches 100% of the time, so that 1k tribal stack of garbage you're about to smash is actually 1k of tribal garbage with a non-hostile 4k stack attached that joins in any and all combat.

If the AI is allied to the player, it wanders around on the periphery of the warzone, taking attrition, not quite knowing which way to go, or what to siege. Eventually, a minor peasant revolt will break out in your allies realm, and he'll about-turn his entire deathstack, march all the way around the mediteranean on some mystical sight-seeing tour, to get from Province to Ravenna, and have his remaining 250 (out of 15,000) starving, out of supplies troops be obliterated by a random, minor revolt in some far-away realm he was marching through.