Complex sentence: Petersen returned to the United States in 1991 and began studying for his BA in Economics at St. Olaf College in Northfield, Minnesota, and in June 1995, after four years of college, Petersen founded Fantasy Flight Publishing.
Split into simpler sentences: Petersen returned to the United States in 1991 and began studying for his BA in Economics at St. Olaf College in Northfield, Minnesota. In June 1995, after four years of college, Petersen founded Fantasy Flight Publishing.