neutralize

Make chemically neutral.

“She neutralized the solution”

Make incapable of military action.

Get rid of (someone who may be a threat) by killing.

“the double agent was neutralized”

Oppose and mitigate the effects of by contrary actions.

Make ineffective by counterbalancing the effect of.

“Her optimism neutralizes his gloom”

Make politically neutral and thus inoffensive.

“The treaty neutralized the small republic”