Prior to 1933 the federal government was relatively small and there was relatively little federal government involvement in the economy. What caused the increase in the size of the federal government and its involvement in the economy was the change in the opinions and feeling of the American people toward the appropriate role of the government and the appropriate role of the United States in world affairs.
Prior to the depression the American people felt that government and the federal government in particular should remain small and for the most part stay out of the economy. With the start of the depression people began to feel that the federal government had a large role in regard to regulation and the providing of safety net services and during World War II people began to feel that it was very important for the United States to maintain a strong military and to be the “leader of the free world.” Because of these changes in the feelings and opinions of the people the elected officials increased the size of government. Elected officials who were willing to increase the size of government were elected and those who were not were not elected. This is how democracy is to work.
The evidence in support of the above is the great change in the fortunes of the Republican and Democratic parties after 1933. After the Civil War and before the depression the Republicans with rare exceptions dominated the national government. This was particularly so during the 1920’s, just before the depression. However, after the depression and the Second World War and until 1981 it were the Democrats who dominated things again with rare exceptions. This change would not have occurred if the people did not tend to favor the policies of the Democrats over those of the Republicans and the policies of the Democrats were for bigger government. Actually in regard to the increase in military spending both the Democrats and the Republicans were for bigger government.
Starting in 1981 Republicans gained back some power, but the size of government was not reduced to any great effect. Also the Republicans did not come to dominate the federal government. Since 1981 power in the federal government has been pretty evenly shared between the two parties. Even in 2012 President Obama was reelected by a majority of the voters even though he was very clearly connected with Obamacare.