What happenes?: I break siege, new army moves in.

[lch]

vfb said:
If the Moving Army is the same nation as the Besieged Army, then the Moving Army and the Besieged Army will group together and fight a single battle against the Sieging Army.

If the Moving Army is the same nation as the Sieging Army, then the Moving Army and the Sieging Army will group together and fight a single battle against the Besieged Army.

If the Moving Army is a third nation, then one of two possibilities can occur, randomly:

1) The Moving Army fights the Sieging Army, and the victor then fights a subsequent battle against the Besieged Army

or

2) The Besieged Army fights the Sieging Army, and the victor then fights a subsequent battle against the Moving Army

Replace all occurences of "besieged army" with "siege breaking army". Battles from movement phase happen like vfb wrote. Then, if there are still commanders left that were set to "storm castle", those proceed to fight the defenders.