Co-operation between nations in its simplest form of bilateral agreements dates back to when States started trading with each other. With time, different types of co-operation began to emerge as the States and the global environment became more complex and more organised. International co-operation among nations is mainly dictated by economic, historical, political, social, cultural, religious, and geographic factors. The Organisation for Economic Co-operation and Development (OECD), the G-8, and the Organisation of Petroleum Exporting Countries (OPEC) are basic examples of economic oriented co-operations. The Commonwealth and the Francophone states give an example of co-operations linked by historical and political factors. The Nordic Councils and Anglo links are examples of co-operation based on social/cultural lines, while the Islamic States form one group based on religious lines.