Complex sentence: Antártica was created on July 11,1961, and was dependent on the Magallanes Province until 1975, when the Antártica Chilena Province was created, making it dependent administratively on Puerto Williams, the province capital.
Split into simpler sentences: Antártica was created on July 11,1961, and was dependent on the Magallanes Province until 1975, when the Antártica Chilena Province was created. It was dependent administratively on Puerto Williams, the province capital.