God is at war with evil, rather, evil is at war with God.

God deals and will deal finally with evil. He considers evil his enemy and adversarial to all of who he is and does. God has turned many of his enemies to be his followers, but there is one, Satan (devil, angel of light, etc.) in particular who is promised complete destruction and any people unwilling to trust in God will join with him in the end for eternal destruction.

Some may think this eternal promise is unnatural or not good, but even the natural world like society and court systems follow suit and do similar punishments through relationships, national wars, and judgments. More often, our human systems tend to be unjust revealing God's justice to be even more just than one may have first perceived. Even so, some may think, feel, and believe that God either is not real because this world is evil or that he's not good because he's left humanity in a swamp of evil. Evil certainly is just that evil - Godlessness (not of God) and ungodliness (twisting God's design). The first Godlessness and ungodliness began in the beginning of the world and recorded in the first part of the Bible, Genesis 3, where an angel and Adam and Eve, became evil - did what is not of God.

Several questions have arisen when many have read these passages and experienced sufferings in this life: 

1. Why did God not prevent evil from coming into existence? The world is God's creation in his sovereign plan and design. He didn't design evil, but he created a world within a time frame in which adversaries were able to arise by being God-less. Within the scope of creation and history, he intentionally made a way to ensure people would eternally live with him reconciled and to be with him forever - therefore, full of God's presence and without evil.
2. Did evil come from God? Evil metaphorically means lacking light and full of darkness or basically meaning God-less. Therefore, by the very word it reveals God is not evil and is only good and holy.
3. Why did God allow evil to continue? God's allowing people to be saved and preserved, therefore, he's being patient until the final day of judgement when evil has it's final end.
4. How can God be just when he allows injustice? If God was to kill all evil, then he would be killing the created people in whom he loves. Therefore, God is justly patient until his people are saved (i.e. redeemed). Therefore, it's not that he's allowing evil to continue, rather, he's scheduled a final end for no one to endure injustice.
5. When will evil stop? Evil stops with and by Him. God cursed the world in Genesis 3 to have a built-in, natural return to dust cycle -- death. This natural, biological breakdown of the body is one way God brings evil to a temporal end until the final end. The most heinous people will and have died. Furthermore, God put eternal wrath and punishment on Jesus instead of humanity that trusts in him so that we would not have to endure what we all deserve -- eternal separation from him and punishment of hell because of it:

By the sweat of your face you shall eat bread, till you return to the ground, for out of it you were taken; for you are dust, and to dust you shall return. - Genesis 3:19

In the Bible's New Testament, right before Jesus came onto the scene, the prophet John the Baptist even warned the Jewish people -- those claimed to be the earthly family of Christ -- that they will be judged accordingly and the righteous judgement was for them to be separated from God for their disbelief in him as they were filled with self-righteousness:

He said therefore to the crowds that came out to be baptized by him, 'You brood of vipers! Who warned you to flee from the wrath to come? Bear fruits in keeping with repentance. And do not begin to say to yourselves, ‘We have Abraham as our father.’ For I tell you, God is able from these stones to raise up children for Abraham. Even now the axe is laid to the root of the trees. Every tree therefore that does not bear good fruit is cut down and thrown into the fire.' Luke 3:7–9

Jesus even warned one of his closest disciples when Peter did not want Jesus to die on the cross:

But he [Jesus] turned and said to Peter, 'Get behind me, Satan (adversary)! You are a hindrance to me. For you are not setting your mind on the things of God, but on the things of man'. - Matthew 16:23

There are countless passages throughout the Bible that record God's promise of a final judgment:

For the Lord loves justice; he will not forsake his saints. They are preserved forever, but the children of the wicked shall be cut off. - Psalms 37:28

For these are days of vengeance, to fulfill all that is written. - Luke 21:22

Beloved, never avenge yourselves, but leave it to the wrath of God, for it is written, 'Vengeance is mine, I will repay, says the Lord'. - Romans 12:19

In flaming fire, inflicting vengeance on those who do not know God and on those who do not obey the gospel of our Lord Jesus. - 2 Thessalonians 1:8

For we know him who said, 'Vengeance is mine; I will repay.' And again, 'The Lord will judge his people'. - Hebrews 10:30

Do you not remember that when I was still with you I told you these things? And you know what is restraining him now so that he may be revealed in his time. For the mystery of lawlessness is already at work. Only he who now restrains it will do so until he is out of the way. And then the lawless one will be revealed, whom the Lord Jesus will kill with the breath of his mouth and bring to nothing by the appearance of his coming. The coming of the lawless one is by the activity of Satan with all power and false signs and wonders, and with all wicked deception for those who are perishing, because they refused to love the truth and so be saved. - 2 Thessalonians 2:5–10

Even throughout history and recorded in the Bible's Old Testament, God wanted his people to be transformed from within and to desire what he desires:

He has told you, O man, what is good; and what does the Lord require of you but to do justice, and to love kindness, and to walk humbly with your God? - Micah 6:8

It may be easy to cast judgement on others to think they will never be in relationship to God and deserve eternal hell, but that is for God's judgement alone and how he has determined:

But love your enemies, and do good, and lend, expecting nothing in return, and your reward will be great, and you will be sons of the Most High, for he is kind to the ungrateful and the evil. Be merciful, even as your Father is merciful. Judge not, and you will not be judged; condemn not, and you will not be condemned; forgive, and you will be forgiven; give, and it will be given to you. Good measure, pressed down, shaken together, running over, will be put into your lap. For with the measure you use it will be measured back to you. - Luke 6:35–38

But I will warn you whom to fear: fear him who, after he has killed, has authority to cast into hell. Yes, I tell you, fear him! - Luke 12:5

The one who rejects me and does not receive my words has a judge; the word that I have spoken will judge him on the last day. - John 12:48

It was to show his righteousness at the present time, so that he might be just and the justifier of the one who has faith in Jesus. - Romans 3:26

Now we know that the law is good, if one uses it lawfully, understanding this, that the law is not laid down for the just but for the lawless and disobedient, for the ungodly and sinners, for the unholy and profane, for those who strike their fathers and mothers, for murderers, the sexually immoral, men who practice homosexuality, enslavers, liars, perjurers, and whatever else is contrary to sound doctrine, in accordance with the gospel of the glory of the blessed God with which I have been entrusted. I thank him who has given me strength, Christ Jesus our Lord, because he judged me faithful, appointing me to his service, though formerly I was a blasphemer, persecutor, and insolent opponent. But I received mercy because I had acted ignorantly in unbelief, and the grace of our Lord overflowed for me with the faith and love that are in Christ Jesus.The saying is trustworthy and deserving of full acceptance, that Christ Jesus came into the world to save sinners, of whom I am the foremost. - 1 Timothy 1:8–15

John records similarly through metaphor and explicitness, in the last book of the Bible for anyone to understand then, now, and the future, to not be concerned with judgment but the judge:

Then I saw heaven opened, and behold, a white horse! The one sitting on it is called Faithful and True, and in righteousness he judges and makes war. His eyes are like a flame of fire, and on his head are many diadems, and he has a name written that no one knows but himself.He is clothed in a robe dipped in blood, and the name by which he is called is The Word of God.And the armies of heaven, arrayed in fine linen, white and pure, were following him on white horses.From his mouth comes a sharp sword with which to strike down the nations, and he will rule them with a rod of iron. He will tread the winepress of the fury of the wrath of God the Almighty.On his robe and on his thigh he has a name written, King of kings and Lord of lords. - Revelation 19:11–16

Behold, I [Jesus] am coming soon, bringing my recompense with me, to repay each one for what he has done. I am the Alpha and the Omega, the first and the last, the beginning and the end. - Revelation 22:12–13

Paul encouraged for people to come to faith in Christ and as Christians, live a life enduring the evil in the world with a heart strength unmatched by the world and only strengthened by him:

Finally, be strong in the Lord and in the strength of his might. Put on the whole armor of God, that you may be able to stand against the schemes of the devil. For we do not wrestle against flesh and blood, but against the rulers, against the authorities, against the cosmic powers over this present darkness, against the spiritual forces of evil in the heavenly places. Therefore take up the whole armor of God, that you may be able to withstand in the evil day, and having done all, to stand firm. Stand therefore, having fastened on the belt of truth, and having put on the breastplate of righteousness, and, as shoes for your feet, having put on the readiness given by the gospel of peace. In all circumstances take up the shield of faith, with which you can extinguish all the flaming darts of the evil one; and take the helmet of salvation, and the sword of the Spirit, which is the word of God, praying at all times in the Spirit, with all prayer and supplication. To that end, keep alert with all perseverance, making supplication for all the saints, and also for me, that words may be given to me in opening my mouth boldly to proclaim the mystery of the gospel, for which I am an ambassador in chains, that I may declare it boldly, as I ought to speak. - Ephesians 6:10–20

Paul additionally encourages people to not fear death:

I tell you this, brothers: flesh and blood cannot inherit the kingdom of God, nor does the perishable inherit the imperishable. Behold! I tell you a mystery. We shall not all sleep, but we shall all be changed, in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised imperishable, and we shall be changed. For this perishable body must put on the imperishable, and this mortal body must put on immortality. When the perishable puts on the imperishable, and the mortal puts on immortality, then shall come to pass the saying that is written: 'Death is swallowed up in victory.' 'O death, where is your victory? O death, where is your sting?' The sting of death is sin, and the power of sin is the law. But thanks be to God, who gives us the victory through our Lord Jesus Christ. Therefore, my beloved brothers, be steadfast, immovable, always abounding in the work of the Lord, knowing that in the Lord your labor is not in vain. - 1 Corinthians 15:50–58

And in the mean time, God is working his will out in the world:

And I tell you, you are Peter, and on this rock I will build my church, and the gates of hell shall not prevail against it. - Matthew 16:18

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