Jehovah's Witnesses are not neutral.
They are citizens of the Watchtower nation state.
The WTBTS acts like a government. It has it's own set of laws, it's own judiciary, it wields the power of punishment over lawbreakers. It tries to control the lives of its citizens as much as any totalitarian govenment that has ever existed. It has it's own system of taxation (head tax at the circut assembly?) and drafts its citizens into compulsory service (field service). Refusal to perform compulsory service is illegal in the watchtower nations state as it is in other nations and will result in legal action by duly constituted authority (elders).
If a watchtower citizen joins the army of another nation he forfeits his rights of citizenship (disassociation) just as the citizen of any country renounces his citizenship by doing likewise.