Why don't countries just merge or join each other? Doesn't all the division simply create more fear and us VS them.
Source: living in a country that run away from bigger brother few decades ago.
The other question is how those tiny kingdoms organise into bigger structures to have economy-of-scale, while still retaining their sovereignty on internal matters.
Just look at Austro-Hungarian Empire, Yugoslavia, etc. You can't force cultures to merge, a problem also acutely experienced in the EU at the moment.