Well, I have a couple comments on that.
1) Islam is not just threatening America or Christians. It's at war with Hindus and Sikhs in India. With Buddhists in Thailand ...with non-Christian Russians. ...with African 'animists'. And, let us not forget that 'post-Christian' Europe is really the main battleground - The Big Show.
2) Christianity isn't a call to arms. And it's not a political or military movement (like Islam). It has more to do with a guiding personal relationship with Jesus.
3) Christianity has definitely been weakened in the West, but is on the move in Africa and China. The new 'West' if you will, is emerging in the South and East.
Having said that, Christians should play a role in confronting Islam because they are in a position to understand the true threat in a way that post-Christians aren't. There is a large spiritual component of this confrontation and atheists/agnostics can't seem to make sense of it.
I have more thoughts on this at
http://www.clashofcivilizations.net BTW, I'm looking for original contributors from all over the world to post their own thoughts on this special-purpose site. If interested, please follow the instructions on the site.
Here is my comment to your comments: Text: Sabine Baring-Gould, 1834-1924
Music: Arthur S. Sullivan, 1842-1900
1. Onward, Christian soldiers, marching as to war, with the cross of Jesus going on before. Christ, the royal Master, leads against the foe; forward into battle see his banners go!
Refrain:
Onward, Christian soldiers, marching as to war, with the cross of Jesus going on before.
2. At the sign of triumph Satan's host doth flee; on then, Christian soldiers, on to victory! Hell's foundations quiver at the shout of praise; brothers, lift your voices, loud your anthems raise. (Refrain)
3. Like a mighty army moves the church of God; brothers, we are treading where the saints have trod. We are not divided, all one body we, one in hope and doctrine, one in charity. (Refrain)
4. Crowns and thrones may perish, kingdoms rise and wane, but the church of Jesus constant will remain. Gates of hell can never gainst that church prevail; we have Christ's own promise, and that cannot fail. (Refrain)
5. Onward then, ye people, join our happy throng, blend with ours your voices in the triumph song. Glory, laud, and honor unto Christ the King, this through countless ages men and angels sing. (Refrain)