Complex sentence: Salem reenlisted for one year on January 1,1776 in the 4th Continental Regiment and for three years on January 1,1777 in the 6th Massachusetts Regiment under Colonel Thomas Nixon (brother of Colonel John Nixon).
Split into simpler sentences: Salem reenlisted for one year on January 1,1776 in the 4th Continental Regiment. On January 1,1777, he re-enlisted for three years in the 6th Massachusetts Regiment under Colonel Thomas Nixon (brother of Colonel John Nixon).