How do nations create international economic communities?

"Nations that frequently trade with each other may decide to formalize their relationship. The governments meet and work out agreements for a common economic policy. The result is an economic community or, in other cases, a bilateral trade agreement (an agreement between two countries to lower trade barriers). For example, two nations may agree upon a preferential tariff, which gives advantages to one nation (or several nations) over others. When members of the British Commonwealth (countries that are former British territories) trade with Great Britain, they pay lower tariffs than do other nations. For example, Canada and Australia are former British territories but still members of the British Commonwealth. You will note that Queen Elizabeth still appears on Canadian currency and the Union Jack is still incorporated into the Australian flag. In other cases, nations may form free-trade associations. In a free-trade zone, few duties or rules restrict trade among the partners, but nations outside the zone must pay the tariffs set by the individual members."