Final answer:
The organizers created a parallel Mississippi Freedom Democratic Party (MFDP) because black voters were prohibited from participating in the Democratic primaries in Mississippi. The MFDP challenged the legitimacy of the white-only Mississippi delegation and the Democratic Party's offering of only a token number of delegates.
Step-by-step explanation:
The organizers believed it necessary to create a parallel Mississippi Freedom Democratic Party (MFDP) because black voters were prohibited from participating in the Democratic primaries in Mississippi. Whites in Mississippi argued that their organization was private and thus exempt from the Fifteenth Amendment. Therefore, African Americans and some white supporters formed the MFDP to challenge the legitimacy of the white-only Mississippi delegation to the 1964 Democratic National Convention. The Democratic Party recognized the white-only delegation and offered the MFDP only a token number of delegates, leading to the creation of a parallel party.