Complex sentence: The first-to-file system is used in all countries, including the United States, which switched to a first-inventor-to-file (FITF) system on March 16,2013 after the enactment of the America Invents Act.
Split into simpler sentences: The first-to-file system is used in many countries,. The United States switched to a first-inventor-to-file (FITF) system on March 16,2013 after the enactment of the America Invents Act.