Simplify the following text for a Grade 7 native English-speaking person.
Original: Some publications in the US have shown this as US territory in the intervening period , and the US Defense Department has stated that the US has a solid basis for a claim in Antarctica resulting from its activities prior to 1959 .
Simplified: The Defense Department of the US Government has also said that there was a solid basis for a claim for the territory . This was because of the activities there before 1959 .