Under ''jus ad bellum'', only legitimate authorities can wage war for the right reasons (usually this means a defensive war) and only as a last resort if every other peaceful means to avert war have been used to no avail. | Under ''jus ad bellum'', only legitimate authorities can wage war for the right reasons (usually this means a defensive war) and only as a last resort if every other peaceful means to avert war have been used to no avail. |