In the OT God used the Hebrews time and time again as implements of His wrath upon nations. But only When God blessed the war usually by His ordering them to attack.
Time and time again when ever the Hebrews took it upon themselves the start a war they where soundly defeated or if they did not follow Gods detailed instructions in how they where to pursue the battle they also suffered as a result.
So engaging in War is only OK when the Lord gives you order to fight.
Now Jesus gave clear teachings in His beatitudes speech that we where not to fight and kill our enemies but where to Love them. You do not love your enemies by putting a bullet in their heads.
Matthew 5:38-39
38 "You have heard that it was said, "An eye for an eye and a tooth for a tooth. 39But I tell you not to resist an evil person. But whoever slaps you on your right cheek, turn the other to him also.
Matthew 5: 43-48
43 "You have heard that it was said, "You shall love your neighbor and hate your enemy.' 44But I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you, 45that you may be sons of your Father in heaven; for He makes His sun rise on the evil and on the good, and sends rain on the just and on the unjust. 46For if you love those who love you, what reward have you? Do not even the tax collectors do the same? 47And if you greet your brethren only, what do you do more than others? Do not even the tax collectors do so? 48Therefore you shall be perfect, just as your Father in heaven is perfect.
Jesus allowed Himself to be killed and blessed those who where killing Him and prayed for them to be forgiven. And a wonderful thing happened on the day of Pentecost when many of these men believed in Jesus and took hold of His grace.
Acts 2
36 “Therefore let all the house of Israel know assuredly that God has made this Jesus, whom you crucified, both Lord and Christ.â€
37 Now when they heard this, they were cut to the heart, and said to Peter and the rest of the apostles, “Men and brethren, what shall we do?â€
38 Then Peter said to them, “Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit. 39 For the promise is to you and to your children, and to all who are afar off, as many as the Lord our God will call.â€
40 And with many other words he testified and exhorted them, saying, “Be saved from this perverse generation.†41 Then those who gladly received his word were baptized; and that day about three thousand souls were added to them.
3000 men forgiven. The Grace of the Messiah Jesus given to those who killed Him. These scriptures are the standard set for followers of Jesus. We Live in an age of grace when The Lord has ordered us to love our enemies and be messengers of His grace to all men even those who would kill us.
The letters of the apostles also confirm the truth:
Romans 12:17-21
17Repay no one evil for evil. Have regard for good things in the sight of all men. 18If it is possible, as much as depends on you, live peaceably with all men. 19Beloved, do not avenge yourselves, but rather give place to wrath; for it is written, "Vengeance is Mine, I will repay," says the Lord. 20Therefore "If your enemy is hungry, feed him; If he is thirsty, give him a drink; For in so doing you will heap coals of fire on his head." 21Do not be overcome by evil, but overcome evil with good.
II Corinthians 10:3,4
"For though we walk in the flesh, we do not war according to the flesh. For the weapons of our warfare are not carnal but mighty in God for pulling down strongholds."
Ephesians 6:12
"For we do not wrestle against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this age, against spiritual hosts of wickedness in the heavenly places."
Ephesians 6:4
"And you, fathers, do not provoke your children to wrath, but bring them up in the training and admonition of the Lord."
Revelation 13:10
He who leads into captivity shall go into captivity; he who kills with the sword must be killed with the sword. Here is the patience and the faith of the saints.
Why do you think thousands of the early Christians went to their executions like lambs to the slaughter? Why did they not resist when they where thrown to the lions in the coliseums of the roman empire? Why because they knew that they where to love their enemies even unto death.
All Praise The Ancient Of Days