Complex sentence: In the last 25 years, for example, Prince George's County, Maryland, in the suburban Washington, DC, area, became majority African American and in 2006 was the wealthiest majority-black county in the nation.
Split into simpler sentences: In the last 25 years, for example, Prince George's County, Maryland, in the suburban Washington, DC area, became majority African American. By 2006 it was the wealthiest majority-black county in the nation.