Why Is There Such A Huge Wage Difference Across States For The Same Type Of Jobs?

The difference in wages for the same jobs across different American states is crazy. Take for example different Police Officers across states. The starting wage of a Police Officer in Jackson, MS is $23,000 a year, rising to about $25,000 after a few years service. While, on the other hand, take a police officer in Annapolis, MD, they start at about $40,000 a year and after a few years service rise to $70,000.
The difference between those 2 wages is rediculous for the same country. Maryland police are paid extremely high wages, while on the other hand Mississippi police are paid about the same as what a Polish or other Eastern European policeman would expect. Seriously, the police earn more in Israel than they do in Mississippi. However, it doesn’t make sense. Jackson is a much bigger, probably more dangerous city than Annapolis, so a Jackson cop has got a much harder job than one from Annapolis.
I am from Australia, and over here nation wide the police have a starting wage of $50,000, which rises to about $90,000 after a few years service.
So can anyone enlighten me as to why there is such a huge difference in pay levels across the US states? I was actually shocked to learn that the average wage in MS is about on par with what poor European countries would receive.
BTW, this isn’t a dig at America or anything, it’s just an observation I’ve made.