After abortive talks between Smith and Wilson in 1966 and 1968, a constitution was agreed upon by the Rhodesian and British governments in November 1971; however, when a British test of Rhodesian public opinion was undertaken in early 1972, black opinion was judged to be against the new deal, causing it to be shelved. The Rhodesian Bush War suddenly re-erupted in December 1972, after two years of relative inactivity, when ZANLA attacked Altena and Whistlefield Farms in north-eastern Rhodesia. After a successful security force counter-campaign during 1973 and 1974, drastic changes in the foreign policy of the Rhodesian government's two main backers, Portugal and South Africa, caused the conflict's momentum to shift in the nationalists' favour. In April 1974, the Portuguese government was overthrown by a military coup and replaced with a leftist administration in favour of ending the unpopular Colonial War in Angola, Mozambique and Portugal's other African territories.