The current Folketing (Danish Parliament) has a 2% electoral threshold for its levelling seats. This means that any party that has received 2% of the national vote share can get into the Parliament.

Under this system, you'd think that the country would experience intense party fragmentation, and while the Folketing does host a relatively large amount of political parties by European standard, these parties tend to be very stable and enduring after several electoral cycles.

The two biggest parties are almost always Social Democrat (center-left) and Venstre (center-right). While the junior partners tend to be the same parties as well. Political parties also consistently coalesce under two major coalitions (i.e. red block and blue block) before election.

How did this stable dynamic come about?