The teaching of Jesus Christ:
Luke 20:21-
21. And they asked him, saying, Master, we know that thou sayest and teachest rightly, neither acceptest thou the person of any, but teachest the way of God truly:
22. Is it lawful for us to give tribute unto Caesar, or no?
23. But he perceived their craftiness, and said unto them, Why tempt ye me?
24. Shew me a penny. Whose image and superscription hath it? They answered and said, Caesar’s.
25. And he said unto them, Render therefore unto Caesar the things which be Caesar’s, and unto God the things which be God’s.
26. And they could not take hold of his words before the people: and they marvelled at his answer, and held their peace.
Romans 13:1-7
Romans 13:1. Let every soul be subject unto the higher powers. For there is no power but of God: the powers that be are ordained of God.
Romans 13:2. Whosoever therefore resisteth the power, resisteth the ordinance of God: and they that resist shall receive to themselves damnation.
Romans 13:3. For rulers are not a terror to good works, but to the evil. Wilt thou then not be afraid of the power? do that which is good, and thou shalt have praise of the same:
Romans 13:4. For he is the minister of God to thee for good. But if thou do that which is evil, be afraid; for he beareth not the sword in vain: for he is the minister of God, a revenger to execute wrath upon him that doeth evil.
Romans 13:5. Wherefore ye must needs be subject, not only for wrath, but also for conscience sake.
Romans 13:6. For for this cause pay ye tribute also: for they are God’s ministers, attending continually upon this very thing.
Romans 13:7. Render therefore to all their dues: tribute to whom tribute is due; custom to whom custom; fear to whom fear; honour to whom honour.
1Peter 2:13. Submit yourselves to every ordinance of man for the Lord’s sake: whether it be to the king, as supreme;
It would appear from above that whether the Christian considers a war just or unjust he is obligated to defend his country if required. That is, no draft dodgers!