In many ways ancient history is one big story of conquest after conquest. One nation totally eliminating another. Even Israelites captured the land of Canaan.

So the question arises. Is conquest of nation condoned by God in any situation, and if so what is that situation?

There is the obvious situation: divine inspiration.

Well obviously, in the case of the Israelites, God TOLD them to go and conquer Canaan, and he was on their side; helping them do it. Were the Israelites the only people God ever fought for and helped conquer? I think not. It is only through his aid that any victory anywhere is made possible, whether the force he fights for is on the defensive and offensive. In every war, every conquest, God is there and has determined the victor at the start. Is that to say that if you win a battle you can know God is on your side? It is true that he helped you achieve that victory, but that doesn't mean that you are 'good' with God or he approves of your lifestyle or goals. He has used conquest to punish the conquered, for example, Babylon conquering Israel. He did not, however, approve of Babylon's ultimate goal, yet he still gave them victory. So yes; God does have a purpose in every conquest, a purpose beyond human purpose, but does he condone one nation massacring another? That depends entirely on the situation, and the only one I am certain of and can ever be certain of is Israel's case.

*nods* Exactly.

This is one of the "tricky bits" in the bible. (period)
Why was it okay for the Israelite nation to take the land from innocent Canaanites?
Why was it okay for the Isrealites to kill the Canaanites?
Why was it okay for the Isrealites to destroy the culture?
As Nomad put it, divine inspiration.
God made the land, it's his. It is perfectly in his rights to take the land away. If the Canaanites had trusted God, he would have found them another home and cared for their needs. However they those to be defiant. They said NO to God. Therefore it was justified for the Isrealites to kill them. As awful as it sounds. Also its worth pointing out that the Canaanites are not innocent.
-Rain

God uses nations to punish nations. Just like Israel was later punished in Babylonian captivity. That doesn't mean Babylon was better than Israel, they were also later destroyed. It's like a circle.