Why does the speaker speak so much about the land?

James Weldon Johnson wrote the poem "Fifty Years" to commemorate the fiftieth anniversary of the Emancipation Proclamation, which freed the slaves in the US, or, in Johnson's words, "struck off our bonds and made us men."
Johnson states that "this land is ours by right of birth / This land is ours by right of toil." This gives some indication as to why he is so concerned with the land itself: as slaves, it was African Americans who "helped to turn its virgin earth" and made the land "fruitful" and prosperous. African Americans have had a closer relationship with the literal earth and land of America than their white compatriots, because they were enslaved for so long and suffered so intensely while farming crops like cotton and corn: "our arms have strained, our backs have burned."
As Johnson states, "we've bought a rightful sonship here/And we have more than paid the price." He points out that it was not due to black men that the Civil War broke out, and that no "black, treason-guided hand" has ever been lifted against the flag or the nation.