The Spanish resented being forced to open their colonial markets, partly due to the prevailing economic theory of mercantilism, which viewed trade as a finite resource. This meant an increase in Britain's share was at the expense of Spain's and wars were often fought over commercial issues. Utrecht had also confirmed British possession of the Spanish ports of Gibraltar and Mahón; their desire to regain them was a factor in the 1718 to 1720 War of the Quadruple Alliance, as well Spanish support for the Jacobite rising of 1719. This made the post of British Consul highly important, held by someone of skill and intelligence.