Not duped. The back-story is that they rose up against the all-powerful government, lost, and were broken into districts. The districts were forced, at threat of destruction/death, to send a male and female child between the ages of 12 and 18 to the games each year as retribution for their uprising and failure. The ultimate story is, they rose up against this oppression and fought back because one person showed them how.
If you haven't read the series, then I don't want to spoil the story about district 13.
Yes, all of that is laid out in the preamble at the beginning of the movie. But when we join the story, most of the districts have bought into the patriotism and honor themes that the rich district has wrapped around the games. They have bought into the system, and that is the problem to be solved. Hope resides in the people of the poorest district since they have the least stake in the system. Their participation is mainly the result of compulsion by the state and economic desparation. This makes them ripe for rebellion if they can only gain consciousness of their own strength and the tenuous nature of the exploiter class’s hold on power.