allow me to pay devils advocate to all of you. name one war that you believe the US entered into for the right reasons.
WW2
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Other points related to your question but which reasons can be argued either way:
Korea: Stopping the spread of communism spurred by an invasion of SK and an attack on American forces
Gulf war 1: Stop Saddam just who invaded Kuwait and threatened Saudi Arabia
Afghanistan: Justifiable response to remove organized terrorist threat support by Afghan government in wake of 9/11
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Don't see much justification in these:
Granada
Vietnam
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Don't know enough about these to argue much about:
WW1
Spanish American War