Long ago, the US military was organized mostly by branches, and they were set against each other so that none of them would challenge the civilian leadership (the founding fathers were paranoid about them taking over).
Some time ago, there was a major reorganization by region. Each command is responsible for a different region and is made up of all of the branches.
My father was stationed at MacDill AFB when the RDJTF became Centcomm (Middle East & North Africa).
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