Complex sentence: It is responsible for U.S. military operations and military relations with 53 African nations--an area of responsibility (AOR) covering all of Africa except Egypt, which is within the area of responsibility of the United States Central Command.
Split into simpler sentences: It is responsible for U.S. military operations and military relations with 53 African nations. Its area of responsibility covers all of Africa except Egypt, which is within the area of responsibility of the United States Central Command.