Pre-emptive strikes are certainly justified when an enemy has decalred himself hostile and to give him time is to give him greater power to strike and kill you.
Policemen do not wait for an armed robber to pull a trigger before shooting them dead. Simply having a gun and showing willingnes to use it is enough to kill them.
Same for Iraq. Hussein was an enemy that vowed to retaliate. he should have been destroped in 1991 not waiting 12 years for him to get stronger and plan new ways to kill Americans.
Thomas Jefferson supported pre-emption, as well.
That is undoubtedly true from a geo-political and military point of view, but I say again: pre-emtpive retribution is not a Christian concept.