this house believes that poverty and dependancy are legacies of colonialism

This is an easy argument for the affirmative IMO. Du have any number of case studies. Africa, India, South America, the Caribbean, even the United States (high population of minorities, especially blacks, is a remnant of the US slave trade). I mean, take your pick.

Africa, though, is perhaps your best example. Deeply in dept to their former colonizers combined with the White Man's Burden leads to dependency aid programs that keeps these nations in poverty.

But I'm not about to do your homework for Du ;). If I were you, I'd check out Africa for my chief example, the state of black Americans in the US as my weakest example, and India and South America as my moderate strength example.