In the late eighteenth century there was a widespread belief that small Republics (classical Athens, ancient Rome, medieval Venice) worked fine, but that large polities (imperial Rome, early modern France) needed a more authoritarian structure. Consequently, documents from the founding era evince a lot of preoccupation with this question, which sometimes leads people to say that James Madison and other founders believed that large democracies couldn’t work. But as Jonathan Bernstein points out this is actually backwards and Madison argued that America’s large size would be a strength.
It’s worth noting, of course, that the idea of “large” and “small” countries is sort of a relative one. Today, you would probably call Finland a small country. But it’s population in 2010 is bigger than the US population in 1790.