How do large party coalition manage to ensure government stability for a fairly long period of time?

Question

I was recently asking about the large coalitions (5+ parties with members in the government) and I was wondering how do they manage to get stable governments with so many parties that have rather different ideologies.

Let's take Finland's example and the following coalition (ideologies also mentioned):

Social Democratic Party -> Social democracy
Centre Party -> Centrism, Liberal Conservatism, Nordic agrarianism
Green League -> Green politics, Pro-Europeanism, Social liberalism
Left Alliance -> Democratic socialism, Eco-socialism
Swedish People's Party -> Social liberalism, Swedo-Finnish interests

Taking a look of the governments list all of them are formed through large coalitions and pretty stable (6 governments in about 10 years).

By contrast taking a look upon Romanian government list, current President alone has observed about 6 different governments and he has just been reelected as a President. What's more, in Romania's case the coalition is typically composed of 2-3 parties.

Question: How do large party coalition manage to ensure government stability for a fairly long period of time?

Answer 1

After a certain point, adding more partners to a coalition makes it more stable. The critical factor is not the total number of partners but the number of major partners. Parties that could make the coalition lose the majority by withdrawing their support.

The current Finnish coalition is not particularly stable, because three out of the five parties are major partners. For a better example, let's look at the coalition that was in place from 2011 to 2015. (The PM changed in 2014, but that is not particularly relevant.) There were initially six parties:

• National Coalition Party: 44 seats (out of 200)
• Social Democratic Party: 42 seats
• Left Alliance: 14 seats
• Green League: 10 seats
• Swedish People's Party: 9 seats
• Christian Democrats: 6 seats

Only the National Coalition Party and the Social Democratic Party were major partners. In a tight spot, only their voices really mattered. The other parties could stay if they believed they had something to gain, or they could leave. The coalition could afford losing any two of the four minor partners.

In the end, that is what happened. The Left Alliance and the Green League left the coalition in 2014. Now the coalition was down to 102 seats out of 200. (There had been some changes in the number of seats due to defections.) All four remaining parties were major partners and the coalition was inherently unstable. The government lasted until the end of its term mostly because the elections were already so close.