1. When you despair, you admit (whether consciously or not) that you don't trust God to care for you or to love you---you're saying that your sins are too great for Him to cover and forgive. You doubt God's goodness and power when you despair. There's a very good reason God gives us assurance again and again in the Bible of His power and love.

2. I think in general, I do agree. Obviously, not every case of someone at war drives the person to confront mortality and morality. But when your life is on the line and you're wondering why you're fighting, it's a lot harder to ignore the questions of right and wrong and who you are and why the war is happening, etc. There is also the issue of being faced with your own limitations and weaknesses.

What does Screwtape mean by "Despair is a greater sin than any of the sins that provoke it?"
I had a little trouble with the statement because I often feel really discouraged and confused that with despair. What Valia says makes sense, if you despair you are saying that God isn't good enough. No matter how discouraged and depressed I get, I still know that God isn't going to abandon me. If I take despair to mean "no hope at all" then it makes sense. (Hopefully, my answer does. )

Screwtape's explanation for war is that it drives humans to a realization of the Enemy. Do you agree?
Yes and no. I can see how people could be forced to rely on and trust in God. War is horrible but God is something they can hope in and get strength from. If people know they could die at any moment, it awakes a desire to know what will happen after death. They also realize how weak they are and how they have very little control over the situation. It shows a need for someone more powerful. On the other hand, I can see how people could look at war and see how cruel it is and come to the conclusion that there is no God.
I think war forces the issue of right and wrong and good and evil. People have do decide what side the think is right or that no side is right.

I had a little trouble with the statement because I often feel really discouraged and confused that with despair.

Ooh, good distinction! I should've made that one, too. There is nothing wrong with being discouraged at times. I believe it was the Puritans who used to talk of "the dark night of the soul", a time when everything would seem really bleak and you'd just feel abandoned. But that time would always be followed by the morning, when you'd feel God's presence again and everything would be brighter for the darkness that you'd been through.
Also, don't forget that Jesus also suffered not from just a feeling that God had removed His presence from Him but from the reality of it on the cross. Jesus cried out, "My God, My God, why have You forsaken me?" and still didn't sin. He also asked for the burden of the cross to be removed from Him beforehand, but He still acknowledged God's will and took it up willingly.
It's interesting to note also in Psalm 22, after the Psalmist talks about how he felt removed from God and alone that he follows it with saying that he knows that God is still there and He is the Holy One. As Christians, we're not supposed to feel happy all the time and never have any doubts. But, part of the important thing, is still trusting and clinging to Christ when we do doubt and struggle.

I hope that all made sense and wasn't too much of a ramble! I definitely needed to clarify what I said before, though, so hopefully that does.

Also, PP, very good point on #2 and how war can also make people turn from God and wonder how a good God could exist if there's all this evil.

What does Screwtape mean by "Despair is a greater sin than any of the sins that provoke it?"
This kind of makes sense, because if we feel that there is no hope left and do not trust in God we end up in a really bad situation. Yes, as Pattertwigs Pal said discouragement is often confused with despair. But we have only to look at the Psalms to realize that discouragement is not a bad thing as long as we lean on God in our discouragement so that it will not turn into despair.

Screwtape's explanation for war is that it drives humans to a realization of the Enemy. Do you agree?
I definitely agree.
War makes a lot of people think about where they will go when they die. A lot of people at the point of death will want to find out if their life meant anything and they will often dwell on the afterlife during times of great turmoil. They will not really be thinking about the life they made on this earth in the text of thinking that they will last forever.

1. Despair, I think, is tied to a loss of hope that things can ever change or get better. In that sense, as others have noted, it reflects a lack of faith in God, or in His character - perhaps distrust in His power to direct history, or in His love, that He actually cares enough to do so on our behalf.

I like the distinction between discouragement and despair. The Psalms are indeed filled with examples. I do think that God can use both discouragement and despair, as He does other 'dark night of the soul' experiences, to ultimately strengthen our faith in Him, and in so doing, bring glory to Himself. I recall several watershed moments in my own life in which things seemed so out of my hands that, despite despair, I was forced to depend upon God and His grace. Those were very hard times to go through but in hindsight they usually were times of immense spiritual growth.

2. A war that directly touches people, like the World Wars did, definitely causes people to realize they're not immortal. Life is fragile and could be lost in the next air raid or an army's attempt to take the next village.

Twigs makes a good point that war can make people think about the 'question of evil' ("How can a good God allow this kind of evil and suffering?"). Finding (or not finding) an acceptable answer to this question could either strengthen one's faith or cause it to be abandoned.

On a slightly lighter note, the rationing imposed during those tough times might have caused people to worry about where their next meal was coming from - but it also discouraged the accumulation of 'stuff' just for the sake of having it. So this too could go either way - by distracting people to seek their daily bread (which we seem to do anyway, even in this land of plenty), or allowing them to see past this to examine the really big issues like life, death, and eternity.

What does Screwtape mean by "Despair is a greater sin than any of the sins that provoke it?"

I wasn't sure what to make of this one. I'm glad other people here could explain it!

Screwtape's explanation for war is that it drives humans to a realization of the Enemy. Do you agree?

I agree that it does drive humans to a realization of God. Is this a proper explanation for why God allows wars? I don't know. I suspect there is more to it though.