The tired old cliché, bang for your buck should be left where it started, with USA politicians discussing the most economic way of killing millions of people.
There is always one, okay on this site a fair bit more. The US is responsible for everything bad in the world. Of course they are as long you ignore the millions killed by Stalin, hell he even managed to kill more than Hitler, hard to achieve but he managed. Then we come to chairman Mao (no doubt one of your hero's) and the culture revolution 49 million? And of course Cambodia a mere 1.7 million. Not many? Well he couldn't beat Mao or Stalin no matter how hard he tried, just not a big enough population. Proportionally he did well 25% of the population. He beat..... well, just about everyone ever. Most importantly he beat your definition of "most economic way of killing millions of people". He got them to dig their own graves and buried them alive. Does that meet your definition of "most economic way of killing millions of people"??