Republicanism in the United States
James Madison, in particular, worried about this, and wrote about it in The Federalist Papers.  The Federalist Papers talk about democracy as being dangerous, because it allows a majority to take away the rights of a smaller group.  However, Madison thought that as more people came to the United States, the country would get more diverse, and it would be harder to form a majority big enough to do this.  In Federalist No. 10, Madison also argued that a strong federal government would help protect republicanism.  The United States' first constitution, the Articles of Confederation, gave most power to the states and had a very weak federal government that could not get anything done.  In Federalist No. 10, Madison argued that a small but powerful group might be able to take control of a small area, like a state.  However, it would be much harder to take over an entire country.  The bigger the country, he argued, the safer republicanism would be.