Abad ke-19 merupakan abad penjajahan oleh kuasa Barat di rantau Asia Tenggara, khususnya British di Sabah. Walau bagaimanapun, penjajahan British di wilayah ini telah mendapat reaksi dan penentangan daripada pelbagai kelompok masyarakat terutamanya di kawasan kota pelabuhan dan estet peladangan. Hal ini kerana, ekonomi kapitalisme yang dibangunkan oleh kerajaan British melalui British North Borneo Chartered Company (BNBCC) sejak abad ke-19 telah melahirkan pelbagai kelas sosial di dua medan ini iaitu golongan inteligensia Melayu dan buruh imigran dari Indonesia. Justeru, pertemuan kelompok masyarakat ini yang terdedah dengan ideologi dan gagasan nasionalisme anti-kolonial dari institusi pendidikan di Tanah Melayu dan Brunei dan lulusan mereka telah membangkitkan kesedaran sosial dan politik serta gerakan nasionalis. Gerakan nasionalisme ini kemudian telah dibangunkan melalui pertubuhan yang mempraktikkan kaedah atau program sosial untuk menggerakkan perjuangan anti-kolonial selepas Perang Dunia Kedua (PDII) seperti Barisan Pemuda (BARIP) yang dibincangkan makalah ini. Makalah ini memanfaatkan sumber-sumber penting dalam arkib peribadi Datuk Zakaria Gunn, seorang pemimpin penting dalam Parti Kebangsaan Melayu Borneo Utara (PKMBU) untuk menelusuri pembangunan nasionalisme di Sabah selepas Perang Dunia Kedua.
The 19th century was a century of colonisation by Western powers in the Southeast Asia region, including the British in Sabah. However, British colonisation in this region has received reactions and opposition from various groups, especially in port city areas and agricultural estates. This is because the capitalist economic system developed by the British through the British North Borneo Chartered Company (BNBCC) since the 19th century has given birth to various social classes in these two areas, such as the Malay intelligentsia and immigrant workers from Indonesia. In fact, the meeting of these groups, who were exposed to the ideology and ideas of anti-colonialism in particular from educational institutions and their alumni in Tanah Melayu, and Brunei, had resulted in social and political consciousness and a nationalist movement. This nationalist movement had subsequently been developed through organisations that practice social principles or programmes to mobilise the anti-colonial struggle after World War (WWII) - one of which was the Barisan Pemuda (BARIP) or the youth movement as discussed in this article. This article uses important sources such as personal documents of Datuk Zakaria Gunn, an important member of PKMBU (Parti Kebangsaan Melayu Borneo Utara) to trace the development of nationalism in Sabah after WWII.