Regarding the people, I think they see wars as a part of the political power struggle within the country and truly believe that the political power struggle is more important to the fate of the nation than the outcome of the war. Presidents get good approval ratings when the war kicks off (See 41 and 43). There is a political interest in the opposition party to remove public support so as to erode the political clout gained by the executive and his party. I think that many in the party truly think that this is in the country's long-term best interests.
Regarding the politicians, I think they (most) are just power-hungry sociopaths. The rest are probably motivated by sentiments similar to the people.
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