I want to join the military but I am with God I am all for him, will I go to Hell if I kill someone while fighting for my country?

If that is the case, then there would be several Popes in hell. More killings have been done in religious wars (the Crusades, etc.).

May I suggest you find a copy of the movie Sergeant York with Gary Cooper. Its about someone wrestling with just this same problem.

No, but can you kill someone ? Read the old testament, God blessed the armies,though the prophets, he ordered the armys to attack. Jesus cured the child of a officer in the Roman army.

The issue is that it is murder. The bible also tells us to follow the lawful commands of our government in the bible also,