Well I broadly agree with you on all of this, you are being a little unfair going with 75 years instead of 100. The longer period would have included the Second World War and maybe that deserves another 5 points for helping defeat the evil Nazi Regime and another 5 points for helping defeat the equally evil Imperial Japanese regime.
Having said that, it was not done purely out of the goodness of their hearts and their belief in freedom and democracy. The USA would have had little influence over a Nazi-controlled Europe. Similarly had Japan been allowed to control all of East Asia, it would have been a serious rival to American hegemony of the planet.
Most military interventions are to extend spheres of influence or at least prevent the sphere shrinking.