The author provides new context in explaining the unsuccessful attempt of Western Christianity to reclaim the Hungarian city of Pest in 1542 in the wider political context of that time. He takes into account the interdependence of other military actions, which took place in parallel and significantly influenced the course of this campaign to Hungary (the French offensive in the Netherlands and Catalonia and the occupation of Brunswick-Wolfenbüttel by troops of the Schmalkaldic League). The vast majority of the Imperial army only passively participated in the brief siege of the city of Pest. The conquest of the city at the beginning of October 1542 was attempted mainly by Hungarian and Italian troops, especially the infantry units of the papal army, which was sent to Hungary by Pope Paul III. Based on a new research of sources from the accounting documentation of the Papal Chamber, the author performs a detailed analysis of the personnel composition of this papal army.