The War between Argentina and Peru–Bolivian Confederation was an armed conflict that occurred between 1837 and 1839. Because it happened simultaneously when the Peru–Bolivian confederation was engaged in a parallel war against the Republic of Chile, in the so-called War of the Confederation, the first conflict referred here is often confused with the second. The war began on May 19, 1837, when the then in charge of managing foreign relations for the Argentine Confederation and governor of the Province of Buenos Aires, Juan Manuel de Rosas, declared war directly on President Andres de Santa Cruz, both for the and its support for the Unitarian Party.