Mikoyan, I welcome your attention to Realms politics, but I fear that in your youthful ardour, you have not looked at the right intelligence reports. Neither Sembia nor Amn have standing armies of any description outside city defence (the nearest thing to it is the Amnian forces stationed in Maztica, but they were mercs), nor do they give a great deal of creedence to military matters. Amn is also quite a distance from Cormyr, and would have to go through the Lords Alliance first.
Also, in the last official installment on the matter, Amn was being overrun by Tethyrian armies and underdark monsters, which was a most silly move IMO (See "Lands of Intrigue)
On the other hand, Cormyr has one of the few standing professional armies in the Realms, even under the official version, and an unparalleled record of recent military triumph (The Crusade, anyone?)
(a note on the versions: My campaign history parts from the TSR line in about 1368, and has a lot of nice stuff happening for the next 24 years. I might dig out some of my stuff one day)
Anyway, as you will remember from your first semester at Evil Dictators college, there is what is known as the Infinite Possibilities Theory, which postulates the existence of parallel dimensions which bear but a passing similarity to one another. Therefore, we are most probably talking about different realms. That is, you would remember if you were listening in class, but I suspect you were off skiving with the Dark Elf Anarchist League, or some other campus group
BTW, Amn is ruled by the Council of Six.
And for dealing with Harpers, I recommend mustard gas or a nice contagion spell. They typically also have trouble when they are not the centre of attention and having a Chaotic Good- loving book written about them.