Conversely, historian James L. Gelvin argues that Palestinian nationalism was a direct reaction to Zionism. In his book "The Israel-Palestine Conflict: One Hundred Years of War" he states that "Palestinian nationalism emerged during the interwar period in response to Zionist immigration and settlement." Gelvin argues that this fact does not make the Palestinian identity any less legitimate: "The fact that Palestinian nationalism developed later than Zionism and indeed in response to it does not in any way diminish the legitimacy of Palestinian nationalism or make it less valid than Zionism. All nationalisms arise in opposition to some 'other.' Why else would there be the need to specify who you are? And all nationalisms are defined by what they oppose."