Why can't the US state police enforce the law across the state?

The police system in the United States is different from that in China.

As a federal country with relatively large state autonomy, the United States does not even have a unified national police agency. The American police are divided into:

1. Federal police: have the right to conduct investigations and arrests in various states of the United States, and the number is small. The most famous is the Federal Bureau of Investigation (FBI) of the Department of Justice of the United States of America, which has 59 branches in states and megacities all over the country.

2. State Police: Police directly subordinate to the state government, whose rights cover the whole state. In highway patrol, there are many policemen at this level.

3. County police, also known as county (county) judicial (public security) officials, whose power is limited to counties (counties);

4. City police: the most common uniformed police in film and television dramas, the criminal police in police stations, and the familiar special police; ;

5. Camp guards: American universities and middle schools have police officers who maintain campus security and have the right to arrest;

6. Types of special police: There are forest police, civil aviation police and marine police, court judicial police and prison guards in the United States. In addition, many law enforcement agencies in the United States allow their staff to carry guns, such as the Federal Immigration and Customs Administration, the Federal Bureau of Alcohol, Tobacco and Firearms, and the Federal Bureau of Health and Food Safety Supervision.

7. Others: The National Guard and China's Armed Police have similar responsibilities, while the Coast Guard is close to the Japanese Coast Guard. Both teams belong to the United States Armed Forces.

The state government sets the power and scope of law enforcement, and the state government pays the law enforcement fees, so the police uniforms vary greatly across the United States (each state has its own uniform and badge style, and even some city policemen in different cities in some States have their own badges). There is almost no intersection between state police in law enforcement. State police can only enforce the law within the state, and all interstate cases are investigated by the Federal Bureau of Investigation (FBI).