The proclamation touched off a series of risings across Java that convinced the British troops entrusted with receiving the surrender of Japanese forces that the self-proclaimed republic was to be taken seriously. At the level of central government, the constitution adopted by republican leaders was presidential in form, but a widely representative Central Indonesian National Committee became, in effect, an ad hoc parliament. Sukarno, as president, agreed to follow parliamentary conventions by making his cabinets dependent upon their ability to command the committee's confidence.

The spontaneous character of the Indonesian Revolution was demonstrated by a number of incidents, notably in the struggle for Bandung in late 1945 and early 1946 and in the Battle of Surabaya in November 1945, in which Indonesian fighters resisted superior British forces for three weeks. Though the Dutch had expected to reassert their control over their colony without question and though they were able to play upon outer-island fears of the Java-based republic, they eventually were compelled to negotiate with republican representatives led by Sjahrir, who by then was prime minister. The Linggadjati Agreement (1946-47), by which the Dutch agreed to transfer sovereignty in due course to a federal Indonesia, appeared to offer a solution to the conflict. (The Dutch claimed that a federation was necessary because of the diversity of the Indies and the difference between heavily populated Java and the more sparsely populated outer islands.) Differing interpretations, however, made the agreement a dead letter from the beginning. In July 1947 the Dutch, in an attempt to settle matters by force, initiated what they termed a police action against the republic. Its effect was to evoke UN intervention in the form of a Good Offices Committee, and it ended in the precarious Renville Agreement of January 1948. In December 1948 a second police action was launched. (see also Index: colonialism)

Meanwhile, the government of the republic faced some domestic opposition. In 1946 a left-wing plot was organized by followers of Ibrahim Datuk Tan Malaka, who opposed the policy of negotiation with the Dutch. This so-called July 3rd Affair was easily crushed. In September 1948 a more serious challenge in the form of a communist revolt (the Madiun Affair) was also defeated.

The second police action aroused American concern. It also closed Indonesian ranks firmly behind the republic. In these circumstances, The Netherlands, at a roundtable conference at The Hague, finally agreed in August 1949 to transfer sovereignty over its colony (with the exception of western New Guinea) to an independent United States of Indonesia in December 1949; a decision about the ultimate fate of western New Guinea (Irian Barat, now Irian Jaya) was to be the subject of future negotiation.