The proclamation of Indonesian Independence by Sukarno and Hatta on 17 August 1945 had immediate effects in Yogyakarta. That afternoon Ki Hajar Dewantoro led a small Taman Siswa group through the streets welcoming the proclamation. The next day Hamengku Buwono sent congratulatory telegrams to the two proclamators and to Dr Rajiman. The first two cables read “I as Jogjakarta-koo extend my congratulations on the proclamation of the Republic of Indonesia and the appointment of Your Excellencies as President/Vice President.” These were followed up with further joint telegrams with the Pakualam, in virtually identical terms. The need for the joint cables suggests some initial lack of coordination.

In early August, with Japanese concurrence, the nationalists had formed a new committee to prepare for the transfer of government powers, called the Committee for the Preparation of Indonesian Independence (Panitya Persiapan Kemerdekaan Indonesia [PPKI]), with membership based on — but smaller than — the BPUPKI. After the proclamation, the committee quickly approved the draft constitution and appointed Sukarno and Hatta as President and Vice President.

The two Yogyakarta leaders sent a congratulatory cable to the Committee, of which Hamengku Buwono's brother Puruboyo was a member. It may seem incongruous now that they also dispatched messages of thanks to Japanese authorities in Jakarta, but at the time this must have seemed a prudent course of action. Hamengku Buwono's statement welcoming the Proclamation contained — for the last time — the ritual thanks to the Japanese which his messages of the past three years had contained. Headed “Let us appropriately repay Dai Nippon's kindness”, the statement pointed out that a strong desire for independence was insufficient in itself and that Indonesia needed to build up the capability to retain independence, bearing in mind that this was “an age of crisis”. Community groups should submerge their narrow interests to create “a comprehensive and strong unity.” Appeals for unity at this early stage only illustrated the fears of disunity which already existed and foreshadowed the difficulty of the task which lay ahead.

The Preparatory Committee confirmed that Java would remain divided into three provinces, but that the kooti s would be separate. The new Department of Home Affairs would manage the public service, the police, land and the principalities. By implication, this placed the principalities under the first Minister of Home Affairs.