"One hundred years of delay have passed since President Lincoln freed the slaves, yet their heirs, their grandsons, are not fully free. They are not yet freed from the bonds of injustice. They are not yet freed from social and economic oppression. And this Nation, for all its hopes and all its boasts, will not be fully free until all its citizens are free."

In this excerpt from President Kennedy's 1963 Civil Rights Address the phrase "the bonds of injustice" most likely refers to:

one hundred years of delay
before President Lincoln freed the slaves
social and economic oppression of their heirs
the hopes and boasts of this nation

John F. Kennedy's 1963 Civil Rights Address revolves around the issue of the African Americans' inability to enjoy the full rights of the white American citizens. In his speech, he addressed the need to allow all rightful citizens of America the right to "enjoy the full and free life which all of us want".

The given excerpt also talks about the dissolving of slavery or racial discrimination by President Abraham Lincoln, but which still persists. He implores on the people to keep the promise of the former president and help make the blacks feel safe. He used the phrase "bonds of injustice" to imply to the hundred years of delay that has been since the emancipation, the years under which they still suffer.