1)
Why did they arrange for war in the opening of the gate?
1.
Malbim (Shmuel II, 10:8): Due to their weakness, they did not want to fight in the field, rather, to take refuge in their fortified city.
2)
Why does it say "Levadam"?
1.
'Rashi', Radak (Shmuel II, 10:8): They split into two camps. Bnei Amon were at Pesach ha'Ir, opposite all of Yisrael. The kings with them were in a camp in the field, in back of Yisrael.
2.
Malbim (Shmuel II, 10:8): Due to their weakness, Amon preferred to take refuge in their fortified city. They were far from Aram in the field.
