Why We Have Two Houses

49 states-- all but Nebraska-- have two-house legislatures.

"The history of ancient and modern republics had taught them
that many of the evils which those republics suffered arose
from the want of a certain balance, and that mutual control
indispensable to a wise administration. They were convinced
that popular assemblies are frequently misguided by ignorance,
by sudden impulses, and the intrigues of ambitious men; and that
some firm barrier against these operations was necessary. They,
therefore, instituted your Senate."

-- Alexander Hamilton (speech to the New York Ratifying Convention,
June 1788)