Christ forgives us for our sins but forgiveness does not prevent us from sinning. Man is sinful by knowing of good and evil. We have free will, and choose to, or are deceived in to sinning. Satan will not help us from ourselves, rather he will exploit our weakness.
War is mass murder, organized sinning. In war there is more than murder. There is often torture, there is theft, and there and there is rape. If by some power, Satan had stopped wars, do you think that this would end all sins? Man murders, steals, rapes, and all sorts of horrors without war. Satan would have to save man from sinning to affect us, and surely Satan will not prevent us from sinning. We must choose to follow the Lord's ordainces, to love Fod and our fellow man. Christ forgives us for our sins but He also ordains that we not sin.
Rev 20:13
13The sea gave up the dead that were in it, and death and Hades gave up the dead that were in them, and each person was judged according to what he had done.
Rev 22:12
12"Behold, I am coming soon! My reward is with me, and I will give to everyone according to what he has done.
Rev 21:8
8But the cowardly, the unbelieving, the vile, the murderers, the sexually immoral, those who practice magic arts, the idolaters and all liarstheir place will be in the fiery lake of burning sulfur. This is the second death."
Clearly, Christ's forgiveness of our sins is not a 'meal ticket' to freely sin, but rather a forgiveness of our imperfection of sinfulness by birth.