The history of internationalism has tended to focus on power centres in the Global North – London, Geneva, New York, Paris – and institutions like the League of Nations, United Nations and UNESCO. What happens when we flip our perspective, and view internationalism from the point of view of the decolonising South? What do we get when we shift our focus from world leaders to the internationalism of activists, intellectuals, feminists, poets, artists, rebels and insurgents operating in Asia and Africa? Moreover, how are our methods of researching and debating international history – in universities, archives and conferences in the Global North – structured by economic inequalities, colonial legacies and visa regimes that limit participation by scholars from the South? This paper considers how we might decolonise both the content and the methods of international history, focusing especially on leftist internationalism and South–South connections in Southeast Asia and the wider Global South.