Help me understand Men at arms

So I understand that MAA work as rock-paper-scissor where they are strong against some and weak against some but do I have to call my MAA into battle separately or do they join the battle when i click "Raise all armies " ?

How do I call them to war ?

Also 'Declare war' screen shows that I have 10000 army but when i click on 'raise all armies' I only have like 1600 (with that red rally tag beside them) ? What's with that ? How do I call my Full Strength ?