Does the Bible forbid going to war?

Is it wrong to join the military?

JWs teach that this verse commands us not to go to war.

Isa 2:4 They will beat their swords into plowshares 

And their spears into pruning shears.

Nation will not lift up sword against nation,

Nor will they learn war anymore.

Christians believe that the above verse talks about the millennium period when Christ will reign on earth. It is talking about the last days as can be seen in the earlier verse of that chapter.

Isa 2:2 2  In the final part of the days,

The mountain of the house of Jehovah

Will become firmly established above the top of the mountains,

And it will be raised up above the hills,

And to it all the nations will stream.

Clearly these verses do not describe our current world. During that time, there will be no more way and so weapons of war become unnecessary. The verses are not an umbrella prohibition to go to war as can be seen from the verses below. These verses say the opposite of Isa 2:4 because we are not living in the time of the millennium reign of Jesus and there is no peace on earth. Nations have to be prepared to protect themselves.

Joel 3

9  Proclaim this among the nations:

‘Prepare for war! Stir up the mighty men!

Let all the soldiers draw near, let them advance!

10  Beat your plowshares into swords and your pruning shears into spears.

Let the weak one say: “I am powerful.”

11  Come and help, all you surrounding nations, assemble together!’”

To that place, O Jehovah, bring down your powerful ones.

Another verse brought up by JWs is the one below.

Matt 26:52 Then Jesus said to him: “Return your sword to its place, for all those who take up the sword will perish by the sword.

Total pacifism is not taught in this Scripture. Indeed, Abraham was blessed by the Most High God ( Gen 14:19 ) after engaging in a war against the unjust aggression of the kings who had captured his nephew Lot. In Luke 3:14 , soldiers come to inquire of John the Baptist about what they should do. John never told them to leave the army. Likewise, Cornelius, in Acts 10 , was a centurion. He was called a devout man (v. 2 ), and the Scriptures say that the Lord heard the prayers of Cornelius (v. 4 ). When Cornelius becomes a Christian, Peter does not tell him to leave the army. Also, in Luke 22:36–38 , Christ says that the one who has no sword should sell his robe and buy one. The apostles responded saying that they had two swords. Jesus responded saying that “it was enough.” In other words, they did not need to get rid of their swords. The Apostle Paul accepted the protection of the Roman army to save his life from unjust aggressors ( Acts 23 ). Indeed, he reminded the Roman Christians that God had given the sword to the king who did not bear it in vain ( Rom. 13:1–4 ). When Jesus returns to earth, He will come with the armies of heaven and will war against the kings of the earth ( Rev. 19:11–19 ). So, from the beginning to the end, the Bible is filled with examples of the justification of war against evil aggressors.

What, then, did Jesus mean when He commanded Peter to put away his sword? Peter was making two mistakes in using his sword. First, while the Bible permits the sword by the government for civil purposes ( Rom. 13:1–4 ), it does not endorse its use for spiritual ends. It is to be used by the state, not by the church. Second, Peter’s use was aggressive, not purely defensive. His life was not being unjustly threatened. That is, it was not clearly an act of self-defense ( Ex. 22:2 ). Jesus appears to have endorsed the use of the sword in civil self-defense ( Luke 22:36 ), as did the Apostle Paul ( Acts 23 ).

(Source: When Critics Ask by Norman Geisler and Thomas Howe)