Gandhi would one day be best remembered for resisting tyranny by using nonviolent ways.
Look at the dictionary entry for the word tyranny.
tyr.an.ny- noun 1. cruel, harsh, authoritarian government 2. a nation ruled by a tyrant, in which one person has ultimate power
Which of the definitions best suits how the word tyranny is used in the sentence?
The British empire treated those in India very harshly and burtually, and were an authoritarian government when they ruled over India, so Defintion 1 fits the best.