The invasion of Corrientes and the Rio Grande do Sul provinces was the second phase of the Paraguayan offensive. In order to support the Uruguayan Blancos, the Paraguayans had to travel across the Argentine territory. In January 1865, Solano López asked Argentina's permission for an army of 20,000 men (led by Gen. Wenceslao Robles) to travel through the province of Corrientes. Argentine President Bartolomé Mitre refused Paraguay's request and a similar one from Brazil.
