Logos

Marshall had the option really, of going for logos, ethos, or pathos.

Pathos seems like it would have been the natural place to go with it, too. He had literal starving children to point to…and nothing makes an emotional argument better than starving kids. (We're tearing up just thinking about it.)

Instead, Marshall laid out his argument methodically. He first pointed out that the situation was bad, then enumerated the ways in which it was bad. This seems like it shouldn't even be necessary, in the sense that no one in the crowd was likely to say, "Wait, war in Europe? When? Why am I always the last to hear about this kind of thing?"

He then pointed out that bad economies is how you get either communism or fascism—and that you really don't want either.

If you're going to make a properly logical argument (which should be your goal even if you aren't trying to convince Mr. Spock to hand you the phaser) you first need to establish your baseline. Think of logic like a house. If you're building it on a swamp, it's just going to sink. Build it on a solid foundation, and what do you know: it stays up.

So with this in mind, Marshall points out that not only has Europe been bombed to a degree heretofore unseen in human history, it was also suffering because pretty much all the powers had turned their economies into wartime versions. That's great for war, but terrible for peace. This also meant that hostiles had broken trading ties across borders, so some of the worst of the economic devastation was invisible.

Then he pointed out that the basic mode of economy, the interplay between the rural farmer and urban manufacturer, had broken down. That mode, basically "farmer feeds the manufacturer, manufacturer equips the farmer," was suffering because there was no currency to trust and no reliable way to get goods anywhere.

Then, he established that the U.S., despite the distance, had skin in the game. You can see the argument building logically from "Hey, there's a problem, here's what happened, here's why it's worse than we think, and here's why it effects us." At this point, the logical build has been achieved.

With his point eloquently and correctly argued, Marshall does maybe the most important thing: offers a solution. He's not whining here. He's a man with a plan. And while maybe you can argue with the specifics of the plan, there's nothing wrong with the man's logic. At its baseline, he's pointing out that economies need money and trust to thrive. His solution? Provide money people trust: the ol' U.S. dollar.