Imperialsim is "the policy of extending the rule or authority of an empire or nation over foreign countries, or of acquiring and holding colonies and dependencies."
The British had conquered Burma in the late 1800s and remained in power until the 1937. Orwell had direct experience as an English officer in India and his time there made him despise the ways in which the British enforced the rules. "Shooting an Elephant" reflects the discomfort Orwell felt about imperalism.
Here is an excerpt from the eNotes pages regarding the historical context of Orwell's disturbing story. You can read more by following the link below.
"Britain, France, and the Netherlands expanded through a series of unplanned acquisitions, burdening the home country with moral guilt and monetary debt, and dissolving as spontaneously as they formed. Something of Johnson’s analysis seems to inform ‘‘Shooting an Elephant,’’ with its air of absurdity and directionlessness. If anyone knew about the tedious minutiae of imperial administration, it was George Orwell, who had been born in India and who served in Burma (1922-27) as a colonial policeman."