Simplify the following text for a Grade 10 native English-speaking person.
Original: Although this appears to have been done by members of this and subsequent expeditions , these do not appear to have been formalized prior to 1959 , when the Antarctic Treaty System was set up .
Simplified: Members of this expedition and later ones seemed to do so , but no official claims were made before 1959 , when the Antarctic Treaty System was set up .