The Paraguayan War refers to the aggressive wars of Argentina, Brazil and Uruguay against Paraguay. The direct cause of the Paraguayan war was that the Brazilian army invaded Uruguay under the pretext of forcing Uruguay to compensate the losses suffered by the so-called Brazilian nationals during the Uruguay civil war in the mid-1950s.
As soon as the armed intervention began, the Uruguayan government appealed to Paraguay for help. Safeguarding Uruguay’s national sovereignty has a stake in Paraguay. Paraguay has a road to the Atlantic coast that passes through Uruguay’s territory. Therefore, it announced its support for Uruguay’s position for a peaceful settlement of the Brazil-Uruguayan conflict. However, the Brazilian army did not stop its armed intervention and occupied Uruguay, forcing Uruguay to join the anti-Paraguayan alliance with Argentina and Brazil. The alliance plots to overthrow the Paraguayan government headed by President Lopez, who actively defends the sovereignty of the country, and seize part of its territory. Great Britain, France, and the United States, which tried to open a channel for the importation of their capital into Paraguay, played a significant role in provoking this Paraguayan war.
The Paraguayan War kicked off in December 1864. At that time, after receiving news that the Allied forces were preparing to invade, Paraguayan President Lopez sent some troops across the Paraguay-Brazil border and occupied the southern part of the Brazilian state of Mato Grosso. The security of the northern part of the country is guaranteed. However, due to the Paraguay fleet's defeat in the battle on the Parana River in June 1865, Paraguay's contact with the outside world was interrupted.
In August 1865, the Paraguayan army captured the city of Uruguayana, Brazil; at the end of August, its 8,000-strong army was surrounded by the Allied forces. After many fierce battles, the remnants of the Paraguayan army were forced to surrender. In May 1866, the Allied forces invaded Paraguayan territory and surrounded the fortress of Umanta. However, it took two years for the Allied forces to conquer the fortress in August 1868. In December 1868, the retreating Paraguayan army was defeated again in the Battle of Piquisiri. In January 1869, the Allied forces occupied Asuncion, the capital of Paraguay. Lopez led the remnants to the Cordillera Mountains and started guerrilla warfare.
In 1869, Lopez added some 12 to 15-year-olds to the army, increasing the number of the army to 13,000. The guerrilla war lasted until the beginning of 1870. Although the Paraguayan army has achieved some victories, it is still continuing to retreat due to the exhaustion of the country's troops and no one to replenish the army. On March 1, 1870, a Brazilian cavalry unit caught up with a small unit led by Lopez in the Sierra Cora area. In the disparity between the widows, Lopez's troops were defeated and he himself was killed. At this point, the military operation ended.
Due to continuous fighting, famine and epidemics, four-fifths of Paraguayan residents died, and only 20,000 men were among the survivors. The Paraguayan League’s troops lost a total of more than 190,000 men.
According to the peace treaties signed with Brazil and Argentina, almost half of Paraguay's territory was taken away. The Brazilian occupation forces were stationed in Paraguay until 1876. This occupation has long hindered the social, political and economic development of the Paraguayan country.
The main reason for Paraguay's failure in the war was that the army of the Anti-Paraguayan Alliance, which received a large amount of assistance from Great Britain, had an advantage in terms of strength and technical equipment.