Comment by sarchertech

The Communist Party, the Social Democratic Party, the German Democratic Party, the Center Party, the German People's Party, the German National People's Party, and the Nazi Party.

Germany is the best argument multiple people in this thread made for how a multiparty system prevents the move towards extremism, but we are within living memory of Germany collapsing into what was arguably the worst case of extremism in history.

Of course there were special circumstances at play. Democracies don’t tend to collapse into dictatorship when things are going great. But the multiparty system did nothing to prevent it.

By the time Hindenburg agreed to dissolve the Reichstag, the SA was powerful enough compared to the German Military and he had enough popular support that he could likely have taken power by force.

If a charismatic demagogue gains enough popular support, no constitution, multi party system, or separation of powers etc can stop him.

You could maybe argue that a demagogue is less likely to rise in a multi party system, but I haven’t seen any empirical evidence to support that.