Simplify the following text for a Grade 6 native English-speaking person.
Original: On the night of the May 18 , 1822 , a mass demonstration led by the Regiment of Celaya , which Iturbide had commanded during the war , marched through the streets and demanded that their commander-in-chief accept the throne .
Simplified: On the night of the May 18 , 1822 , a mass of people marched through the streets . They demanded that their commander-in-chief Iturbide accept the throne .