Simplify the following text for a Grade 13 native English-speaking person.
Original: On December 6 , 1798 , the French under Joubert occupied Turin and forced Charles Emanuel to abdicate all his territories on the Italian mainland and to withdraw to the island of Sardinia , which stayed out of the reach of the French army .
Simplified: In December 1798 , the French occupied Turin and forced Charles Emmanuel to abdicate all his territories on the Italian mainland and to withdraw to the island of Sardinia .