This is a old question on this board, tired of talking about it, so I will copy and paste something for now.
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"Should a Christian join the military?"
q.gif (1639 bytes) Does Jesus or the New Testament condemn or embrace a man joining the army?
a.gif (1659 bytes) Abraham had his servants trained to fight in battle if the need arose, and the need did. Genesis 14:14-16 says, “And when Abram heard that his brother was taken captive, he armed his trained servants, born in his own house, three hundred and eighteen, and pursued them unto Dan. And he divided himself against them, he and his servants, by night, and smote them, and pursued them unto Hobah, which is on the left hand of Damascus. And he brought back all the goods, and also brought again his brother Lot, and his goods, and the women also, and the people.â€Â
At times, God told His people to fight against other peoples and nations. 1 Samuel 15:18 says, “And the LORD sent thee on a journey, and said, Go and utterly destroy the sinners the Amalekites, and fight against them until they be consumed.â€Â
Romans 5:6-8 refers to the nobleness of a person being willing to die for others. “For when we were yet without strength, in due time Christ died for the ungodly. For scarcely for a righteous man will one die: yet peradventure for a good man some would even dare to die. But God commendeth his love toward us, in that, while we were yet sinners, Christ died for us.†So it is noble when a person is willing to risk his life for others.
There is a caution for the Christian, when considering today’s military service as a career, and not just as a service when the need arises for war. The caution deals with the ungodly atmosphere in today’s military. Proverbs 13:20 says, “He that walketh with wise men shall be wise: but a companion of fools shall be destroyed.†1 Corinthians 15:33 says, “Be not deceived: evil communications corrupt good manners.†There is the cursing, the immorality, the sleeping together of males and females in the same tents or quarters on the battlefield today, etc. You have to face many of the same things in many other occupations, but at least you can go home to your own place and have a godly atmosphere there. Many soldiers have fallen to immorality with the present practice of males and females living, working, and sleeping in the same quarters.
There is also another factor to consider. When you sign up for the military, you are placing your life in the hands of others. You will go where they say. You will do what they say. You will live where they say. You will fight whom they say. You will take orders from whom they say (even if it is a United Nations mission and you are under the authority of a foreign officer?). 1 Corinthians 7:20-23 says, “Let every man abide in the same calling wherein he was called. Art thou called being a servant? care not for it: but if thou mayest be made free, use it rather. For he that is called in the Lord, being a servant, is the Lord's freeman: likewise also he that is called, being free, is Christ's servant. Ye are bought with a price; be not ye the servants of men.â€Â
Many Christian men have joined the military forces and have served with great distinction and spiritual maturity. They have been great influences upon those that they have worked with or commanded. But there have also been many young men from Christian families who joined the military, and have been made spiritual shipwrecks: their lives scarred by alcohol and immoral living.
Each young man should carefully and prayerfully discern God’s perfect will for his life, before signing on to military service. He should make sure that he has specific Scripture leading him  not just his feelings.http://www.libertygospeltracts.com/question/prequest/miltserv.htm
