In the 1990s, about twenty civil wars were occurring concurrently during an average year, a rate about ten times the historical average since the 19th century. However, the rate of new civil wars had not increased appreciably; the drastic rise in the number of ongoing wars after World War II was a result of the tripling of the average duration of civil wars to over four years. This increase was a result of the increased number of states, the fragility of states formed after 1945, the decline in interstate war, and the Cold War rivalry.