He was a big landlord who lorded it over the whole area.
Tips
usage
The pair is 一方 and 双方 'both sides'; the other side is 另一方 or 对方. In the 'region' sense it appears in 称霸一方 'to dominate a region' and the saying 一方水土养一方人 'each place's land and water raise its own kind of people'.
mistakes
Before a noun, 一 + 方 is often just a number and the measure word for square things: 一方手帕 'a handkerchief', 一方印章 'a seal'.