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Source:Welch:Exemption from Military Duty:people of Ammon...the grant of this exceptional privilege was consistent with ancient Israelite law
John W. Welch: "people of Ammon...the grant of this exceptional privilege was consistent with ancient Israelite law"
John W. Welch,
The only Book of Mormon group given an exemption from military service was the famous people of Ammon. In repenting of their previous shedding of blood, they had sworn an oath that they would never again take up arms (see Alma 24:11-13). After they arrived in Zarahemla, they were granted an extraordinary exemption from active military duty if they would help to sustain the Nephite armies with provisions (see Alma 27:23-24). Surprisingly, the grant of this exceptional privilege was consistent with ancient Israelite law. —(Click here to continue) 
- John W. Welch, "Exemption from Military Duty," Reexploring the Book of Mormon (1992)