political arena vs sphere

political arena and sphere both are nouns.

Word	Noun	Adjective	Verb	Adverb
political arena	Yes	No	No	No
sphere	Yes	No	No	No

As nouns, sphere is a hypernym of political arena; that is, sphere is a word with a broader meaning than political arena:

Other hypernyms of political arena include area, arena, domain, field, orbit.

political arena (noun)	sphere (noun)
a sphere of intense political activity	any spherically shaped artifact
	a particular aspect of life or activity
	the geographical area in which one nation is very influential
	the apparent surface of the imaginary sphere on which celestial bodies appear to be projected
	a solid figure bounded by a spherical surface (including the space it encloses)
	a three-dimensional closed surface such that every point on the surface is equidistant from the center
	a particular environment or walk of life