Assuming you mean the military of the USA, in the 1920s the US military engaged in a series of military interventions called Banana Wars in order to keep the economic climate in the area friendly to American commercial interest. They were called Banana Wars because the main interest was from fruit companies. In the 1930s FDR's Good Neighbor Policy toned down American involvement in the area.
Liberal democracy proved to be a failure due to many economic problems that the world faced and the way that wars were being handled. People understood that government should have higher power in order to make sure that things like the great depression doesn't happen, while also understanding that a mass militarization is necessary in order to be capable of fighting a war as great as the first world war.
