History
Bicameral vs. Unicameral Legislatures: Design and Implications
Quick fact
While nearly all federal systems (like the US, Germany, and India) use bicameralism, many unitary states (like Sweden and New Zealand) have successfully adopted unicameralism, and no major fully democratic federal state has a unicameral national legislature.
Why this is interesting
Most of the world's democracies have two legislative chambers, yet some of the most stable and efficient governments operate with just one. Why?