With the British declaration of Emergency in 1948 and a crackdown on parties of the Malay Left and the MCP the ability of the PKMM to operate was much reduced. API was the first organisation to be banned and nationalist leaders such as Ahmad Boestamam, Ishak Haji Muhammad, Katijah Sidek and Burhanuddin Al-Helmy were imprisoned. In the aftermath PKMM activism splintered. Some retired from political activity altogether, others sought to generate political change from within UMNO itself, with former KMM and PKMM member Mustapha Hussein losing to Tunku Abdul Rahman by one vote in the contest for the Chairmanship of UMNO. Others such as Shamsiah Fakeh, Wahi Anuwar and Musa Ahmad fled to the jungles and allied themselves with the community guerilla war against the British. Whilst others would go onto found or lead other nationalist, socialist or Islamist political parties. Thus upon their release Ahmad Boestamam would found the Parti Rakyat whilst Ishak Haji Muhammad would found the Labour Party, both would later go on to found the Parti Marhaen Malaysia, whilst Burhanuddin Al-Helmy would go onto lead the Parti Islam Se-Malaysia from 1956 to his death in 1969.