Final answer:
The Democrats held power from 1932 to 1968 primarily due to the New Deal, which revigorated the economy and expanded their voter base, and civil rights reforms that attracted a diverse electorate.
Step-by-step explanation:
The Democrats were the party in power between 1932 and 1968 due to several factors, including economic policies leading to prosperity and effective social and civil rights reforms. The pivotal change came with Franklin D. Roosevelt's New Deal, a series of programs designed to revive the economy, stimulate economic development, and generate employment opportunities during the Great Depression.
Additionally, the Democrats' support for civil rights reforms gained them the loyalty of an increasingly diverse voter base, including African Americans who switched their allegiance from the Republican Party to the Democratic Party, attracted by federal jobs offering equal wages regardless of race.
The New Deal Coalition, which included union workers, African Americans, and other minority groups, gave the Democrats a significant electoral advantage. Their support for job-producing projects, such as the Works Progress Administration (WPA) and the Tennessee Valley Authority (TVA), fueled their widespread popularity, leading to a long-term shift in voter allegiances. However, as civil rights reforms moved to the national stage, rifts between northern and southern Democrats began to emerge, and many southern Democrats shifted allegiance to the Republican Party in the following decades.