Of a surface being equivalent approximately the fifth of France, Bulgaria has an extremely varied geography : vast plains in north at the edge of the Danube, of the mountainous chains (Balkan which crosses of is in west the country, Rila and Pirin in south-west, and Rhodopes in the south), of the valleys in the center and south-west. The mountains, which occupy approximately 25 % of the territory, are less present, in Bulgaria, which in the other Balkan States. The nature of the relief explains the extent of the cultivable grounds (42 % of the territory) and allowed the development of the irrigation in the plains. The cities are almost exclusively Bulgarian (with, however, some districts Tziganes), but certain rural areas are populated as a majority of Turks. Agricultural country before the Second World war, and relatively low in mining and energy resources, Bulgaria knew a strong industrialization for the communist period.