Complex sentence: In 1995, when President Bill Clinton signed Executive Order 12958 regulating national security classification and declassification which established a system to declassify automatically information more than 25 years old, unless the government took discrete steps to continue classification of a particular document or group of documents.
Split into simpler sentences: In 1995, when President Bill Clinton's Executive Order 12958 regulated national security classification and declassification. It established a system to declassify automatically information more than 25 years old, unless the government took discrete steps to continue the classification of a particular document or group of documents.