special relativity - Why are the electric force and magnetic force classified as electromagnetism?

I confuse the four kinds of fundamental interactions, so I think the electric force and magnetic force should not be classified as a big class called electromagnetism.

Here is my evidence:

1. 
   

   The Gauss law of electric force is related to the surface integration but the Ampere's law corresponds with path integration.

   
   


2. 
   

   The electric field can be caused by a single static charge while the magnetic force is caused by a moving charge or two moving infinitesimal current.

   
   



3. 
   

   The electric field line is never closed, but the magnetic field line (except those to infinity) is a closed curve.

   
   

Answer

Consider this: A charged particle at rest creates an electric field, but no magnetic field. Now if you walk past the charge, it will be in motion from your point of view, that is, in your frame of reference. So your magnetometer will detect a magnetic field.

But the charge is just sitting on the table. Nothing about the charge has changed.

Evidently the space around the charge is filled with something that at times appears to be a pure electric field, and at other times appears to have a magnetic field. We conclude that the field is something other than an electric field or a magnetic field. It is another type of field which combines the two into one entity.