Four years later in 1941, amid fast-growing tensions within disputed territories around the Zarumilla River, war broke out with Peru. Peru claimed that Ecuador's military presence in Peruvian-claimed territory was an invasion; Ecuador, for its part, claimed that Peru had recently invaded Ecuador around the Zarumilla River and that Peru since Ecuador's independence from Spain has systematically occupied Tumbez, Jaen, and most of the disputed territories in the Amazonian Basin between the Putomayo and Marañon Rivers. In July 1941, troops were mobilized in both countries. Peru had an army of 11,681 troops who faced a poorly supplied and inadequately armed Ecuadorian force of 2,300, of which only 1,300 were deployed in the southern provinces. Hostilities erupted on July 5, 1941, when Peruvian forces crossed the Zarumilla river at several locations, testing the strength and resolve of the Ecuadorian border troops. Finally, on July 23, 1941, the Peruvians launched a major invasion, crossing the Zarumilla river in force and advancing into the Ecuadorian province of El Oro.