What war? 
We are in a war. We've been born into it. The moment we accept Christ – evil is our enemy. We wage war against every crime, all deceitfulness, all suffering, and every human battle that has ever been fought – whether with angry voices, courtroom tricks, swords and spears, guns and tanks, or bombs and missiles. These are the earthly manifestations of a cosmic war that has been going on since Satan's rebellion. 

The origins of this war are described in Revelation 12:7-9: 

And there was a war in heaven, Michael and his angels waging war with the dragon. And the dragon and his angels waged war, and they were not strong enough, and there was no longer a place found for them in heaven. And the great dragon was thrown down, the serpent of old who is called the devil and Satan, who deceives the whole world; he was thrown down to earth, and his angels were thrown down with him.

A major objective in this war is to advance truth. We have to fight for it. There are places in this world where you couldn't find out the truth even if you were willing to buy it. There are places in this world where you'd be in trouble if you spoke the truth. Truth is a cause that someone has to fight for. To the degree that we are free, it is because someone fought tor and paid a price for truth. 

Ultimately, we have to choose which side we're on. We say either: "There is such a thing as truth," or "I don't know, and I don't care." But we are all forced into the choice; we can't be neutral. Neutrality is an alliance with evil. 

This spiritual war is inherent in the Great Commission. Jesus said, "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit, teaching them to observe all that I commanded you" (Matthew 28:19, 20).

The Great Commission invites active hostility. Not everyone wants to be a disciple. Jesus didn't say, "Go and disciple all those except those that don't want it." He said to go to all the nations.