end of the year, a de facto balance of power or even "situation of routine" had developed between Portuguese and PAIGC forces. Meanwhile, however, PAIGC had launched a flurry of political activity – having judged in roughly 1971 that independence was feasible and even imminent, its leadership had begun preparing for independence, including by creating new domestic political structures (with elections held in 1972) and by conducting an intense diplomatic offensive abroad. Assassination of Amílcar Cabral: January 1973 After years of attempts by Portugal to attack or capture Cabral as a means of undermining PAIGC's organizational structure, Cabral was assassinated on 20 January 1973 in Conakry, by disgruntled PAIGC members. PAIGC purged the traitors, and regrouped under the joint leadership of Aristides Pereira and Luís Cabral, Amílcar's half-brother. Rather than disabling the group, the assassination of PAIGC's leader was followed by some of its most ambitious offensives, as it destroyed or took over key Portuguese positions in the north and on the southern border. Having acquired new weaponry, and in particular new ground-to-air missiles, PAIGC began in March 1973 to attack with vigour the Portuguese Air Force, "effectively neutralising" Portugal's air superiority – which until then had been Portugal's most marked tactical advantage, and a significant one given Guinea's difficult ground terrain. As PAIGC deployed its new ground-to-air missiles, as well as new large-caliber mortars and rockets (reportedly from Soviet-bloc suppliers), the war "increasingly took on a 'conventional' rather than guerrilla character". In July 1973, PAIGC artillery destroyed the important Portuguese strongpoint of Guileje, which previously had been held by an elite garrison of 400 mostly European troops and which had presented a major obstacle to PAIGC's communications with the government in Guinea-Conakry. By then, Portuguese forces were largely confined to the major cities and a diminished collection of fortified camps, and the Portuguese strategy increasingly amounted to little more than – in the phrase of Portuguese officer Major Carlos Fabião – "holding on as best as possible" ("aguentar enquanto fosse possível"). It launched no further offensives in the war. End of Portuguese rule in Guinea Unilateral independence: September 1973 On 23–24 September 1973, the People's National Assembly (Assembleia Nacional Popular de Guiné) met in Madina do Boé, near the border with Guinea-Conakry, and declared the independence of the Republic of Guinea-Bissau. The Assembly comprised 120 delegates, overwhelmingly from PAIGC, who had been appointed following elections held by PAIGC in