Roughly the size of Western Europe, the Democratic Republic of the Congo is one of the world's leading producers of copper and cobalt and is a sizable producer of diamonds, gold and rare earth minerals. Mining is the country's biggest contributor to total export revenue and to government revenue via taxes on those exports and on industry income. Total industry revenue from annual exports is estimated to be $4.4 billion, of which copper and cobalt exports account for roughly $3.4 billion. Annual crude oil production generates approximately $500 million worth of exports and diamonds generate about $220 million. The government's share of total revenue similarly depends on mineral exports. Taxes on copper and cobalt mining alone have contributed roughly $450 million of the estimated $800 million generated in annual mining income taxes. Taxes on crude oil production, which total approximately $327 million, are the next largest contributor in the extractive industry to annual government revenue. Following the Congo's independence in 1960, authorities in the colonial capital, Kinshasa, took over colonial infrastructure and assumed the mantle of national sovereignty — but that sovereignty did not go unchallenged for long. Within two weeks of the Congo's independence in June 1960, the province of Katanga declared its own independence, a bid defeated in 1963 through the deployment of U.N. peacekeepers. The concentrations of copper and cobalt found in Katanga make for a tenuous relationship between Kinshasa and provincial authorities roughly 1,600 kilometers (1,000 miles) away in Lubumbashi. Attacks continue by independence-oriented militias in Katanga province — for example, militants launched an attack on army and police in Lubumbashi on March 23 that left 35 civilians dead. Although the government cannot ignore these mining regions or abandon these revenues to rebel or rival hands — such revenues have long sustained rebel and armed group activity in the Congo — Kinshasa lacks the capability to unilaterally impose order in a region that is even farther from its seat than Katanga is.