That principle is just fine in terms of DEFENSIVE wars at home, but not OFFENSIVE or PRE-EMPTIVE wars such as the one we are engaged in with Iraq.The principle is: "And again, the Lord has said that: Ye shall defend your families even unto bloodshed. ....to defend themselves, and their families, and their lands, their country, and their rights, and their religion." Alma 43:47
The Book of Mormon is full of examples and principles showing that the Lord was often with the Nephites when they were defending themselves from the Lamanites who came into their land. While they were waging a defensive war the Lord often protected them, but when the Lamanites decided to go unto the Lamanites (OFFENSIVE/PRE-EMPTIVE) that is when the Lord stopped helping them:
from Mormon Chapter's 3 & 4:
"...the Lamanites did come down to the city of Desolation to battle against us; and it came to pass that in that year we did beat them, insomuch that they did return to their own lands again... because of this great thing which my people, the Nephites, had done, they began to boast in their own strength, and began to swear before the heavens that they would avenge themselves of the blood of their brethren who had been slain by their enemies.
"....they did aswear by the heavens, and also by the throne of God, that they would go up to battle against their enemies...
"...I, Mormon, did utterly refuse from this time forth to be a commander and a leader of this people, because of their wickedness and abomination...
"...I [Mormon] utterly refused to go up against mine enemies; and I did even as the Lord had commanded me; and I did stand as an idle witness to manifest unto the world the things which I saw and heard, according to the manifestations of the Spirit which had testified of things to come.
"...the Nephites did go up with their armies to battle against the Lamanites, out of the land Desolation... the armies of the Nephites were driven back
"...And it was because the armies of the Nephites went up unto the Lamanites that they began to be smitten; for were it not for that, the Lamanites could have had no power over them.
"...from this time forth did the Nephites gain no power over the Lamanites, but began to be swept off by them even as a dew before the sun."