Surely the Lord was fighting for Israel

Joshua 10:1-43
After an all-night march from Gilgal, Joshua took them by surprise.
The Lord threw them into confusion before Israel, so Joshua and the Israelites defeated them completely at Gibeon. Israel pursued them along the road going up to Beth Horon and cut them down all the way to Azekah and Makkedah. 
Joshua subdued the whole region, including the hill country, the Negev,the western foothills and the mountain slopes, together with all their kings. He left no survivors. He totally destroyed all who breathed, just as the Lord, the God of Israel, had commanded.
Surely the Lord was fighting for Israel!
The treaty with the Gebeonites promptly involves Israel in war. All five Amorite kings are killed at Makkedah and their city-states (all except Jerusalem) destroyed in the campaign following the rout at Beth-horon. All the strategic cities of the south fall before Joshua's army.
Israel now controls the land from Kadesh-barnea in the south to Gaza on the west, and as far north as Gibeon.
The long day is usually taken as an extension of daylight, but it may be a prolongation of darkness. An eclipse of the sun has been suggested.
How?
Surely the Lord was fighting for us when we follow his command.