The late 1920s witnessed the rise of Sukarno to a position of prominence among political leaders. He became the country's first truly national figure and served as president from independence until his forced retirement from political life in 1966. The son of a lower priyayi schoolteacher and a Balinese mother, Sukarno associated with leaders of the Indies Party and Sarekat Islam in his youth and was especially close to Cokroaminoto until his divorce from Cokroaminoto's daughter in 1922. A graduate of the technical college at Bandung in July 1927, he, along with members of the General Study Club (Algemene Studieclub) established the Indonesian Nationalist Union (PNI) the following year. Known after May 1928 as the Indonesian Nationalist Party (PNI), the party stressed mass organization, noncooperation with the colonial authorities, and the ultimate goal of independence.

Unlike most earlier nationalist leaders, Sukarno had a talent for bringing together Javanese tradition (especially the lore of wayang theater with its depictions of the battle between good and evil), Islam, and his own version of Marxism to gain a huge mass following. An important theme was what he called "Marhaenism." Marhaen (meaning farmer in Sundanese) was the name given by Sukarno to a man he claimed to have met in 1930 while cycling through the countryside near Bandung. The mythical Marhaen was made to embody the predicament of the Indonesian masses: not proletarians in the Marxist sense, they suffered from poverty as the result of colonial exploitation and the islands' dependence on European and American markets. Beyond the goal of independence, Sukarno envisioned a future Indonesian society freed from dependence on foreign capital: a community of classless but happy Marhaens, rather than greedy (Western-style) individualists, that would reflect the idealized values of the traditional village, the notion of gotong-royong or mutual self-help. Marhaenism, despite its convenient vagueness, was developed enough that by 1933 nine theses on Marhaenism were developed in which the concept was synonymous with socio-nationalism and the struggle for independence. Mutual self-help in diverse contexts became a centerpiece of Sukarno's ideology after independence and was not abandoned by his successor, Suharto, when the latter established his New Order regime in 1966. Considering himself a Muslim of modernist persuasion, like Ataturk in Turkey, Sukarno advocated the establishment of a secular rather than Islamic state. This understandably diminished his appeal among Islamic conservatives in Java and elsewhere.

The Minangkabau Sutan Syahrir (1909-66) and Mohammad Hatta became Sukarno's most important political rivals. Graduates of Dutch universities, they were social democrats in outlook and more rational in their political style than Sukarno, whom they criticized for his romanticism and preoccupation with rousing the masses. In December 1931 they established a group officially called Indonesian National Education (PNI-Baru) but often taken to mean New PNI. The use of the te7fc term "education" reflected Hatta's gradualist, cadre-driven education process to expand political consciousness.

By the late 1920s, the colonial government seemed to have moved a long way from the idealistic commitments of the Ethical Policy. Attitudes hardened in the face of growing Indonesian demands for independence. Sukarno was arrested in December 1929 and put on trial for sedition in 1930. Although he made an eloquent speech in his own defense, he was found guilty and sentenced to four years in prison. His sentence was commuted after two years, but he was arrested again and exiled to the island of Flores, later being transferred to the town of Bengkulu in Sumatra. In April 1931, what remained of the PNI was dissolved. To replace the PNI, the Indonesia Party (Partindo) was soon established and, in 1932, Sukarno and thousands of others joined it. Partindo called for independence but was repressed by the Dutch and it dissolved itself in 1934. After Japanese forces occupied the Netherlands Indies in March 1942, however, Sukarno was allowed to reenter the political arena to play a central role in the struggle for independence.

Data as of November 1992