From the start of the Second Intifada, which began in September 2000, Nablus became a flash-point of clashes between the IDF and Palestinians. The city has a tradition of political activism, as evinced by its nickname, "jabal al-nar" (Fire Mountain) and, located between two mountains, was closed off at both ends of the valley by Israeli checkpoints. For several years, movements in and out of the city were highly restricted. The city and the refugee camps of Balata and Askar constituted the center of "knowhow" for the production and operation of the rockets in the West Bank.