Neutrality during war-time makes it impossible to defend a nation against the treachery of aggressor nations.
In the twentieth century Germany invaded Belgium, Italy invaded Greece, and the UK occupied Iceland.
Neutrality has broken down as a feasible state for nations. Few if any can stand wholly apart from war. Neutral country air space may be overflown by satellites or spy planes, or by ballistic missiles. Nuclear weapon detonation, furthermore, will expose neutral nations to radioactive fall-out and ecological destruction. The fragility of the status is indicated by the Charter of the United Nations which allows for the revocation of neutrality of states that the Security Council calls upon to take coercive measures against acts of aggression (Articles 41 and 48). International trade links may involve neutral nations in the provision or transit of strategic materials or general, favourable economic trade with antagonists. For all these reasons, plus the sweeping aside of neutrality by aggressor nations, the position may be an unrealistic and untenable one
The absence of neutral nations would be on obstacle to mitigating some of the effects of war and would eliminate those who could best act as go-betweens and peace-makers.