The location of a country can also be a factor. Take Singapore for example. It’s a small island but plenty of international trading goes on there (not taking other forms of businesses into consideration for this example) due to its location.

I quote, “The port’s location at the crossroads of the main shipping routes has facilitated the Republic’s development into a principal centre for shipping activities in Southeast Asia. It is a focal point for some 400 shipping lines linking Singapore to more than 700 ports in 130 countries worldwide. There are about 1,000 ships in the port at any one time”. That’s from: http://www.singaporemirror.com.sg/ab_infr_port.htm

I hope that was kinda helpful.

Also, since the Swiss don’t do much, or have many natural resources, they handle a lot of Intl Banking. Also, they stay neutral in any war going on around the world, which is why many people fled Germany in WWII to Switzerland.

It also goes for countries that are islands, like Australia.

Hope this helps, question was a little vague…