How to fight Fomoria?

[bgifu]

I am in a MP with the single age complete and CBM1.5.
I am with LA Tien Chi and my capital is close to the Fomoria.It's only turn 8 now.We have a few provinces and low research.
The bless of Fomoria is about 6E4S4N.The giant is so difficult to kill.Is there some strategy to fight Fomoria in early game?

And second question about the map move

(ONE) ( TWO)

(THREE) ( FOUR)


There are four provinces: one, two, three, four.
One, three are the friendly provinces.Three, four are in the enemy territory.There are armies in the each province.
My army in the one and three move to the two and the army of enemy in two and four move to the three.
What will happen?

In the manual:
There is a battle in the enemy province between the two armies;
There is a battle in your province between the two armies;
The armies miss one another and exchange places.

Which event occurs depends on the size of the armies in question and the terrain involved.

How to explain the last sentence?What is the detail about the size of the armies and terrain ?