The relationship between Pozzo and Lucky illustrates well the complexities of the relationship between England and Ireland. At first glance, Pozzo (England; the colonizer) leads Lucky (Ireland; the colonized) around by the throat, forcing him to go where he leads, at the pace he leads. Pozzo insults Lucky by calling him names and threatening to sell him to a stranger in town. Lucky endures the abuse, even crying at the thought of being separated from Pozzo. However, a closer examination of the duo reveals that they are indeed interdependent.
Lucky attends to Pozzo's every whim and carries all of his baggage. This could be viewed as a reference to Ireland as the workhorse of the British Empire, providing nearly all of the food for England. (As an example, the Irish Potato Famine starved out so many in Ireland because the English would not reduce their dependence on Irish agriculture, taking just as much from the country as before the blight.) As Ireland served as the agricultural force for England, it was still dependent on England for military protection and industry.
One could argue that the interdependence between the two is only the result of a corrupting force, i.e. imperialism. England is only dependent on Ireland because it outsources its agriculture and has no means of feeding its people without them; Ireland cannot defend itself because it was taken over by force by the British military, which now protects it. Pozzo alludes to this circular fate by reasoning that he could have been the slave if circumstances were different.