A key player on the world stage and a country at the political heart of Europe, France paid a high price in both economic and human terms during the two world wars. The years that followed saw protracted conflicts culminating in independence for Algeria and most other French colonies in Africa as well as decolonization in Southeast Asia. In 1958, the mixed nature of the coalition government structure collapsed as a result of the tremendous opposing pressures generated by four years of war with Algeria, bringing General de Gaulle to power again, heading the government to prevent civil war. Marking the beginning of the Fifth Republic, General de Gaulle became prime minister in June 1958 and was elected president in December of that year. In recent years, French-German cooperation has proved central to the economic integration of Europe, including the introduction of a common exchange currency, the euro, in January 1999. But French voters rejected the proposed EU constitution in a referendum in May 2005. Overall, the French economy is highly developed. It is one of the largest economies in the world, and is the third largest in the European Union. The country's economic strength lies in its substantial agricultural resources, a large industrial base, and a highly skilled workforce.