We are called to follow the law and our law permits this in the Declaration and 2nd Amendment. Our founders made this clear.
It is the right of the citizen to protect their country from foreign AND domestic threats.
The Bible doesn't condemn one from serving their country. I choose to serve the cause of the loyalist to the America that millions have fought and died for to protect.
The Bible has commands for the individual, the family, the church, and government. And good government in scripture is told to bring justice against evil while protecting the innocent. If it is a bad government then they are going against the will of God. God will judge them just as the Ottoman Empire fell, just as the Nazi regime fell, just as the Imperial Japanese Army fell, just as the Soviet Union collapsed. God sent armies against them.