The NDP was banned by Ian Smiths white minority government, and it was subsequently replaced by the Zimbabwe African Peoples Union (ZAPU), also founded by Nkomo and Mugabe, in 1962, itself immediately banned. ZAPU split along ethnic grounds a year after its formation, with Robert Mugabe breaking away with the Shona majority, forming, with Ndabaningi Sithole and Herbert Chitepo, the Zimbabwe African National Union, leaving ZAPU as a mostly Ndebele organisation.
Nkomo was detained in 1964, with fellow revolutionaries Mugabe and Sithole, until 1974, when they were released due to pressure from South African president B.J. Vorster. He went to Zambia to fight for Zimbabwean independence.
A majority rule government of Zimbabwe Rhodesia led by Abel Muzorewa was formed in 1979 between Ian Smith and Ndabaningi Sithole's ZANU, which by now had also split from Robert Mugabe's more military ZANU faction. However, the civil war waged by Nkomo and Mugabe continued unabated, and Britain and the USA did not lift sanctions on the country. Britain persuaded all parties to come to Lancaster House in September 1979 to work out a constitution and the basis for fresh elections. Mugabe and Nkomo shared a delegation, call the Patriotic Front (PF), at the negotiations chaired by Lord Carrington. Elections were held in 1980, and to most observers surprise Nkomo's ZAPU lost in a landslide to Mugabe's ZANU. Nkomo was offered the ceremonial post of President, but declined. He was appointed to the cabinet, but in 1982 was accused of plotting a coup. Mugabe unleashed the notorious Fifth Brigade upon Nkomo's Matabeleland homeland, in an operation termed Gukurahundi.
In 1987 Nkomo was reconciled with Mugabe and two parties merged into Zanu-PF, leaving Zimbabwe as effectively a one-party state, and leading some Ndebeles to accuse Nkomo of selling out. In a powerless post, and with his health failing, his influence declined until his death in 1999.