What is the difference between burning and gassing people in ovens and doing it to a whole nation out in the open?

What is the difference between burning and gassing people in ovens and doing it to a whole nation out in the open?

在炉子里焚烧和用毒气毒死人，以及在户外对整个国家这样做有什么不同?

-- Norodom Sihanouk 西哈努克