Answer:
Sending troops to ensure African Americans could enroll
Step-by-step explanation:
Governor Wallace was the Governor of Alabama when the Federal Government tried to ensure that African Americans enroll in the University of Alabama, the Governor challenged the authority of the federal government under President Lyndon because he was not satisfied with the decision of the Federal Government he blocked the registrars doorway so that African Americans could't access it.
The president responded by sending troops to ensure African Americans could enroll. and forcefully enforce the order in the process