Final answer:
The direct primary system was widely adopted following the election of 1920, reflecting a movement towards more democratic candidate selection and a response to disillusionment with party-controlled nominations.
Step-by-step explanation:
Although introduced during the Progressive Era, the direct primary was widely adopted by the national parties after what some might consider a 'disastrous event'. When reviewing American political history, the most prominent event that catalyzed the widespread adoption of the direct primary system was the election of 1920. This election followed a period of Progressive Era reforms and occurred in the context of the collapse of the Progressive Party, the weakening of the Democratic Party, and a general dissatisfaction with the two major parties' control over candidate selection.
The direct primary system emerged as a response to a desire for more democracy and transparency in candidate selection. It replaced a system where party officials and delegates at conventions had exclusive control over which candidates were presented to the public. By establishing primary elections, party members gained the ability to vote directly for their preferred nominees, increasing the influence of public opinion over party elites.