and, after his sudden death, Batlle's nephew, Luis Batlle Berres, became the President. In 1949, to cover the British debt for the beef deliveries during WWII, British owned railroads and water companies were nationalized. The 1951 constitutional referendum created the Constitution of 1952 which returned to the collective executive model and the National Council of Government was created. The end of the large global military conflicts by mid-1980s caused troubles for the country. Because of a decrease in demand in the world market for agricultural products, Uruguay began having economic problems, which included inflation, mass unemployment, and a steep drop in the standard of living for the workers. This led to student militancy and labor unrest. The collective ruling council was unable to agree on harsh measures that were required to stabilize the economy. As the demand for Uruguay's export products plummeted, the collective leadership tried to avoid budget cuts by spending Uruguay's currency reserves and then began taking foreign loans. The Uruguayan peso was devalued, inflation reached 60%, and the economy was in deep crisis. The Blancos won the 1958 elections and became the ruling party in the Council. They struggled to improve the economy and advocated a return to strong Presidency. After a constitutional referendum, the Council was replaced by a single Presidency under the new Constitution of 1967. The elections of 1967 returned the Colorados to power, and they became increasingly repressive in the face of growing popular protests and Tupamaros insurgency. The Tupamaros were an urban guerrilla movement formed in the early 1960s. They began by robbing banks and distributing food and money in poor neighborhoods, then undertaking political kidnappings and attacks on security forces. They occupied a city near Montevideo in an operation known as the Taking of Pando. Their efforts succeeded in first embarrassing, and then destabilizing, the government. The US Office of Public Safety (OPS) began operating in Uruguay in 1965. The US OPS trained Uruguayan police and intelligence in policing and interrogation techniques. The Uruguayan Chief of Police Intelligence, Alejandro Otero, told a Brazilian newspaper in 1970 that the OPS, especially the head of the OPS in Uruguay, Dan Mitrione, had instructed the Uruguayan police how to torture suspects, especially with electrical implements. Military dictatorship, 1973–1985 President Jorge Pacheco declared a state of emergency in 1968, and this was followed by a further suspension of civil liberties in 1972 by his successor,