Lilmod,
1. I wrote that it is a machloket. I do not remember where but see Shoftim ch. 11 that Sichon acquired part of Ammon by conquest and that this acquisition gave him legal ownership. Thus, Israel was not violating the commandment not to take land from Ammon when it took this area.
2. My point is that states have rights that individuals do not have. An individual may not imprison someone to prevent crime and certainly may not kill someone for that purpose.