Let's limit the size of countries to 35 million to make people happier?

See the World Happiness Report 2017.
Any common point between the top 10.
They have no more than a dozen of millions of citizens...

4M in NZ, 5M in Finland, Switzerland 8M, Australia 23M, Canada 35M, the biggest.
It makes me think something simple.
Small countries make people's life happier.
They are constantly praised in media, I recently saw Elon Musk praising Norway (fr).
Some think the city is where things will change (fr). I agree and disagree at the same time. A lot of cities are at the same time doing great things for the planet and to offer a great way of life but they also gentrifying, kicking poor outside. So what's the point...

I think it's definitely complicated to make a big country happy. The 14th of the ranking seems to make me lie, it's the USA. But his ranking is due to its richness per capita. And we know most of the countries richness goes to the top 1%. Moreover, the USA is not a country it's a group of states working together. Biggers state is California, 39M then Texas 27M. So it validates my idea of limiting the size of countries/states to 35ish :)

Let's limit the size of countries to 35 million?
It means splitting the France into 2 to 3...