A common question and one that many churches are divided over is whether or not Christians should join the military. Some churches don’t mention it at all, other churches forbid members to join the military. The short answer from PCOR9: It depends. Now for the long answer:
Cornelius, a centurion (they controlled about 100 men in the Roman army), was given the gospel and received the Holy Ghost. We cannot say whether he gave up being a centurion but it is said that he may have become a leader in the early church (which would probably hint to him giving it up). Either way, it can be possible for those in the military to serve God.
Acts 10:1-2, 44 KJV
There was a certain man in Cæsarea called Cornelius, a centurion of the band called the Italian band ,
 A devout man , and one that feared God with all his house, which gave much alms to the people, and prayed to God alway.
 While Peter yet spake these words, the Holy Ghost fell on all them which heard the word.
Then we have Peter in the garden. When Peter pulled out his sword ready to fight, Jesus told him to put it away. Now we understand that even they who do not fight can still be killed, but was it not Jesus that said not to be afraid of the ones that kill the body but fear Him who can kill the soul (Matthew 10:28).
Matthew 26:51-56 KJVS
And, behold, one of them which were with Jesus stretched out his hand, and drew his sword, and struck a servant of the high priest’s, and smote off his ear.
 Then said Jesus unto him, Put up again thy sword into his place: for all they that take the sword shall perish with the sword.
 Thinkest thou that I cannot now pray to my Father, and he shall presently give me more than twelve legions of angels?
 But how then shall the scriptures be fulfilled, that thus it must be?
 In that same hour said Jesus to the multitudes, Are ye come out as against a thief with swords and staves for to take me? I sat daily with you teaching in the temple, and ye laid no hold on me.
 But all this was done, that the scriptures of the prophets might be fulfilled. Then all the disciples forsook him, and fled.
As Christians, we are supposed to be fighting a spiritual war. How does it look when we worry more about fighting man’s war instead of putting on the armor of God and fighting the real adversary. Aren’t we as Christians supposed to be a body of believers? The Church is made up of believers all over the world and yet instead of being peaceful, we are filled with anger or value the income more than a burden. Perhaps we can focus more on helping the world, not cause more damage. What were we called to do? To be a witness of Christ and to proclaim the gospel.
In the end, the question is not can you but should you (1 Corinthians 10:23). Should a Christian join the military? I think the decision comes down to between you and God. You are personally responsible for yourself, not your pastor (but it may be that your pastor doesn’t want to see you end up another death statistic). You live for you (and hopefully God and your family). It’s your choice, but I would ask that you consider what PCOR9 has said, read your Bible, and ask God during prayer what He wants you to do.