Business
Where the ruling family itself goes into trade, instead of looking down on it and leaving it to a merchant caste, a small kingdom can build ports, shipyards and sea routes. The rise of a port is then a joint project of rulers, their officials and the merchants, not of merchants working alone.
Merchants who build up wealth through long-distance trade can end up paying for the everyday running of governments. Over time their role moves from trading goods to keeping the state funded and working.
Overseas trade can flourish while a large empire is collapsing. The weakening of central rule did not stop these regional merchants, and their trade boomed in exactly those years.