Why Only Two Parties in the US, But Nine in Norway?

How the US voting system reduce the number of parties and how voting systems in other countries give more selection to voters.

The Norwegian Parliament. It has 169 representatives of which 150 are selected from Norway’s 19 provinces.

Why is it so difficult to vote a third party into power in the US? This isn’t simply a cultural phenomenon. Almost every time I see a discussion of this in social…