Historically, Christian thought has taken a number of approaches to war.
Christianity and violence - Wikipedia
I guess it depends on the “history” you are consulting.
“Christendom’s” approach to war is not the same as that which was promoted by Christ and his apostles.
e.g.....Jesus pronounced “happy” (or blessed) those who were were peaceable (or literally “peacemakers”) A peacemaker is not just a “peacekeeper” because a Christian was not to take up arms against anyone.
2 Corinthians 10:3-6...
“3 For though we walk in the flesh, we do not wage warfare according to what we are in the flesh. 4 For the weapons of our warfare are not fleshly, but powerful by God for overturning strongly entrenched things. 5 For we are overturning reasonings and every lofty thing raised up against the knowledge of God, and we are bringing every thought into captivity to make it obedient to the Christ;”
Romans 12:17-21...
“
17 Return evil for evil to no one. Take into consideration what is fine from the viewpoint of all men. 18 If possible, as far as it depends on you, be peaceable with all men. 19 Do not avenge yourselves, beloved, but yield place to the wrath; for it is written: “‘Vengeance is mine; I will repay,’ says Jehovah.” 20 But “if your enemy is hungry, feed him; if he is thirsty, give him something to drink; for by doing this you will heap fiery coals on his head.” 21 Do not let yourself be conquered by the evil, but keep conquering the evil with the good.”
Jesus said....
”You heard that it was said: ‘You must love your neighbor and hate your enemy.’ 44 However, I say to you: Continue to love your enemies and to pray for those who persecute you, 45 so that you may prove yourselves sons of your Father who is in the heavens, since he makes his sun rise on both the wicked and the good and makes it rain on both the righteous and the unrighteous.” (Matthew 4:43-45)
Can you see a single point in those verses where a Christian is ever given permission to shed blood?
We all know Christianity isn't a passivist religion and nor should we expect it to be. Imaging if the USA had not responded to the Pearl Harbor attack from the Japanese or the British had not resisted Nazi Germany.
If one is relying on God and his word, then history is already cast. Imaging that God was not in control and seeing a necessity to take matters into their own hands is why Israel got themselves into trouble, causing God to withdraw from them because of their lack of faith.
How can a worshipper of the true God ever imagine that he is not in control of what is going on here? What he allows is what he allows. He gives us no permission to interfere.
The world alienated from God will do what it wants....but only with his permission, and only so far as it serves his purpose. Misunderstanding the reasons why God has done what he has in the past, leads to confusion and disobedience. Understanding what God did back then will help us discern what he will do in the future. (All recorded for us in scripture) God has to allow mankind to take themselves to the brink of extinction before they get the message that mismanagement in self-governance, their hostile attitudes towards their fellow man (especially when demonstrated along racial or religious lines) and even detrimental decisions in their personal lives, is all part of the greatest object lesson that we will ever be given.
We will all be caught in the act of being ourselves, determining our own future by how we live this life. That is how I understand the state of the world down through history. All recorded for posterity and as precedents set for all time to come. God’s Kingdom will “come” as Jesus said it must.....ready or not. (Daniel 2:44)
The prerogative towards passivism is present in some groups including a minority of Christian sects.
It is simply a matter of obeying the one we claim to serve....not finding excuses to ignore him.
There is no doubt war results in unimaginable harm and all efforts towards peaceful resolution need to be made but sometimes war is necessary and the God of the Christian Bible has commanded it if some of the OT stories are anything to go by.
Using OT accounts of war is pointless. We are not under the old law covenant, nor are we contained in a God-given land, whose borders need to be defended. The only wars fought in OT times were to demonstrate the superiority of the God of Israel over the false gods of the nations who sought to take Israel’s territory.
The Diaspora meant that the Jews were no longer contained in one place but were dispersed into other lands. When Jesus walked the earth, there was no land that belonged to Israel and they had no military force. They had been gobbled up by the Roman Empire and were under their laws. This is in keeping with Daniel’s prophesy concerning the march of world powers. Jesus never once involved himself in politics or encouraged his disciples to fight for the freedom of his people. He said that “the appointed times of the nations” had to run their course. There were more world rulers to come, leading to our own time.
The Jews had no authority to execute anyone so they needed the help of the Roman government to have Jesus executed, despite the fact that Pilate found him innocent of any capital offence.
Nationalism certainly has contributed to the expansionist behaviours of some notable countries during the twentieth century and beyond. I don't see a problem with having pride in one's country but that can certainly become excessive and harmful. I quite like the NZ national anthem!
Having a love of one’s homeland is natural, but nationalism and its conjoined twin (patriotism) can lead people to sacrifice their Christianity for their nationality. A Christian has no “nationality” (Acts 10:34-35) because we see ourselves as citizens of God’s kingdom, never being placed in a situation where we would kill our own brethren over divisive political, racial or religious issues.
If a national anthem is a hymn, (a prayer set to music) then it has religious connotations like saluting a flag.....like it or not, it involves worship. We will not compromise our worship by participating in those things. We want to remain neutral, like Jesus taught us to be.