To be a soldier or to serve in the military was actually originated from the days of old and that's why the Bible has everything to say about it
2 Timothy 2:4 (KJV) No man that warreth entangleth himself with the affairs of this life; that he may please him who hath chosen him to be a soldier.
If we look at some verses in the Bible we would see that even GOD himself encouraged David during the time of king Saul
1 Samuel 17:37-49 (KJV) David fighting against the Philistines
Joshua 4 is talking about the victory from Jericho and it involves soldiers.
We Christian's are soldiers of Christ. We fight against every principalities,power of darkness and God gives us victory.
We are in the military of God.
From the days of old, serving in the military or in the army was very vital. And wars that were fought by the children of God, God himself supported them.
To be in the military is no sin,it is biblical.
Thanks and God bless you all.