Battle of Paraguarí
1811 CE.
Shown on the map at -25.633°, -57.150°.
The Battle of Paraguarí, also known as Battle of Cerro Porteño, took place on January 19, 1811 nearby Paraguarí between the army sent by the Primera Junta and the forces of the Intendency of Paraguay under the command of their governor Bernardo de Velasco. The battle ended with a Paraguayan victory and boosted confidence to declare independence from both Buenos Aires and Spain.
Text from the Wikipedia article Battle of Paraguarí, licensed CC BY-SA 4.0.