Webb, Kieran (2007). "The Continued Importance of Geographic Distance and Boulding's Loss of Strength Gradient". Comparative Strategy. 26 (4): 295–310. doi:10.1080/01495930701598607. S2CID153451707.
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Webb, Kieran (2007). "The Continued Importance of Geographic Distance and Boulding's Loss of Strength Gradient". Comparative Strategy. 26 (4): 295–310. doi:10.1080/01495930701598607. S2CID153451707.