In 1882, Nikola Tesla discovered the prinicple of a rotating magnetic field. He began an endeavor to operate machines based on this principle, particularly his famous ac motor which allowed for the efficient and long distance distribution of electrical energy. Prior to Tesla's creation, motors operated by continually passing a conductor through a magnetic field that was stationary. Tesla's suggestion was to remove the commutators(electrical switches that periodically reversed the current in an electric motor), and thus allow the machine to operate on a rotary field of force.

How does Motor Works?
An electric motor works in a simple way. An electric current is passed through a magnetic field. The electrons are passed through a loop and make the motor spin. The force of North and South Pole of electromagnetic pushes the coil to turn around and thus rotate the coil continuously. Tesla's motor used to passed through an AC current which later on proved to be the most beneficial current.

References
PBS Tesla Master of Lighting
Tesla Memorial Society
PBS Tesla Master of Lighting: AC vs DC
PBS Tesla Master of Lighting: Polyphase Power
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/mothow.html