Belgrano then went on a diplomatic mission to Europe along with Bernardino Rivadavia to seek support for the revolutionary government. He returned in time to take part in the Congress of Tucumán, which declared Argentine Independence (1816). He promoted the Inca plan to create a constitutional monarchy with an Inca descendant as Head of State. This proposal had the support of San Martín, Martín Miguel de Güemes, and many provincial delegates, but was strongly rejected by the delegates from Buenos Aires. The Congress of Tucumán approved the use of his flag as the national flag. After this, Belgrano again took command of the Army of the North, but his mission was limited to protecting San Miguel de Tucumán from royalist advances while San Martín prepared the Army of the Andes for an alternative offensive across the Andes. When Buenos Aires was about to be invaded by José Gervasio Artigas and Estanislao López, he moved the Army southwards, but his troops mutinied in January 1820. Belgrano died of dropsy on 20 June 1820. His last words reportedly were: "¡Ay, Patria mía!" (Oh, my country!).