Ricardo's law is the advantage of specialization. If A can produce more value by producing X instead of Y, it is best to produce the former and buy the latter - that efficiency in production creates a possibly counter-intuitive extra for both trading parties.

«In this kind of economy, communities specialize in producing certain goods in order to participate in the regional exchange system [...] they see their efforts are better spent in producing other products to exchange for desired goods made in other villages or regions. [...] development of a regional economic system rooted in exchange networks among communities underpinned the peaceful heterarchical metal age socio-political system that endured in Thailand for over two millennia»