This article explains theoretically, and demonstrates empirically, the instrumental role of the balance of capabilities in shaping the form of warfare that develops in civil wars. It contends that the current common practice of labelling civil wars as either ‘guerrilla’ or ‘conventional’ (which is usually meant to accurately characterise the type of warfare throughout an entire civil war) is unable to fully encapsulate the dynamic nature of warfare in civil war. It is instead argued that the form of warfare frequently varies significantly across time and space in a single conflict. This article is divided into three sections. Section one examines recent advances in the understanding of warfare in civil wars. It identifies three categories of warfare in civil war: conventional, guerrilla and irregular. Section two builds on previous studies to develop the concept of the balance of capabilities. Finally, the article illustrates these theoretical insights through a discussion of the American and Somali Civil Wars.