Agricultural production is the sector that contributes the least to Angola's economy, a mere 13 percent of the GDP. Prior to the civil war in 1975 Angola was self-sufficient in food production and was a major exporter of agricultural products. The two most important products for export prior to the war were coffee and sisal. Angola was the second-largest producer of coffee in Africa and the fourth-largest in the world in 1974. Today only 3 percent of all arable land is being cultivated. There are two crucial reasons for this. First, large numbers of refugees have fled the country due to constant fighting, leaving the land uncultivated. Secondly, the vast amounts of anti-personnel mines that have been buried throughout the countryside make it difficult to cultivate the land again. This is unfortunate because Angola has the potential to grow a huge range of both semi-tropical and tropical crops. With continued fighting, Angola cannot fulfill its promise as a major agricultural producer.