Anybody who can read realizes these terms are NOT synonomous or interchangeable. The Kingdom of [or from] God is eternal. Being eternal it has no beginning or ending. It definately is not the same as the Kingdom of [or from] Heaven. The Kingdom of [or from] Heaven had a very definate beginning and it began with the birth of the King, Jesus Christ.
The belief these two terms are synonmous and interchangeable springs largely from trinitarian theology. If God=Jesus then out of necessity Kin