While the former Spanish colonies may have rejected Madrid’s rule, they accepted the doctrine of uti possidetis juris de 1810, the notion that newly minted republics would accept as their frontiers the boundaries that Spain had used to delineate its former colonies. Agreeing on boundary lines proved quite complicated because over the years various military, religious, and political organizations had created often conflicting versions of the same maps. As Chile’s Diario Oficial noted, the cartographers often had only a vague idea where the boundaries lay. The frontier separating Bolivia and Chile, for example, ran through the Atacama Desert, one of the world’s more desolate territories. During their early years neither Bolivia nor Chile had disputed too vigorously the precise location of their common border: the ownership of a few feet of an arid wasteland simply could not excite even the most avid jingo. But thanks to the discovery of guano and, later, nitrates, both highly prized sources of chemicals needed to manufacture fertilizer and explosives, the Atacama suddenly became alluring. Consequently, beginning in the 1860s Santiago and La Paz began to press their claims to this potential economic bonanza: Bolivia demanded the land down to the twenty-fifth parallel south latitude, and Chile, the territory north to the twenty-third parallel south latitude. Anxious to assert its sovereignty, Santiago’s minions occupied Mejillones in 1861, replacing the ousted Bolivian officials with Chileans who issued rights to mine the guano in the disputed area. In 1863 Bolivia’s legislature, eager to assert its claim to the desert, gave the president, Gen. José María de Acha, permission to use force if Chile refused to recognize Bolivian sovereignty over the disputed land.
The border issue might have plunged the nations into a war but for an unexpected revival of imperialism: an 1864 Spanish scientific expedition, in fact a naval task force, used the supposed maltreatment of its citizens as an excuse to seize Peru’s Chincha Islands. The incident so inflamed both Chile and Bolivia that they set aside their own squabbles to repel the Spanish invasion. Pending a final solution, the border was drawn on the twenty-fourth parallel. Eventually, Peru’s coastal batteries in Callao drove Madrid’s fleet from South American waters but only after it had seriously damaged Chile’s principal port, Valparaíso. With peace restored to the Pacific, a new Bolivian government under Gen. Mariano Melgarejo tried again in 1866 to solve the boundary issue. Santiago, perhaps in thrall to the spirit of “Americanism,” agreed to accept the twenty-fourth parallel as the border. Chile, however, retained the right to share equally in the revenues generated by anyone exploiting those minerals mined in the territory located between the twenty-third and twenty-fifth parallels.
By the early 1870s numerous Chile-based companies mined not only guano but also, increasingly, nitrates from the Atacama. Similarly, Chilean interests also extracted from Bolivia’s Caracoles mines silver ore, which they sent to Chile, where it was smelted, processed, and then exported to Europe. Believing itself to be the victim of greedy Chilean capitalists, the Bolivian legislature decided to protect their nation’s economic future by seeking more control of its desert resources. It began by nullifying Melgarejo’s 1866 pact.
Normally, the Chileans would have responded aggressively, but the Chilean government, feeling threatened by Peru’s recent naval rearmament program and Argentine territorial demands, considered it prudent to resolve peacefully its dispute with Bolivia. Thus, Chile’s new president, Federico Errázuriz, sent Santiago Lindsay north to La Paz with orders to settle the boundary issue. The resulting 1872 accord, the Lindsay- Corral pact, seemed almost a repeat the 1866 agreement, although La Paz did agree to include nitrates as one of the minerals that Chileans could mine duty free in return for some financial concessions. Not surprisingly, many Bolivians feared that the Lindsay-Corral pact would not truly inhibit Chile from attempting to control the contested area: obviously Bolivia needed more than words to keep its territory out of Chile’s clutches. Bolivia quickly discovered an anti-Chilean soul mate in Peru, which viewed Errázuriz’s decision to acquire two armored warships as jeopardizing its maritime interests. Thus, in February 1873 Bolivia and Peru signed a secret military agreement pledging to aid each other if Chile threatened either signatory.
Perhaps emboldened by this alliance, the Bolivian congress refused to ratify the Lindsay-Corral accord. Errázuriz, fearful that Bolivia and Peru might entice Argentina to join their anti-Chilean coalition, again compromised: in August 1874 Bolivia and Chile again set the boundary between their territories at the twenty-fourth parallel. Chile surrendered its territorial claims and its right to share any revenues derived from taxing enterprises mining the Atacama, and in return the Bolivian government vowed not to raise taxes on any Chilean corporation mining the desert for a period of twenty-fi ve years. Some Bolivian deputies wanted to reject the treaty, but the threat of the then president, Tomás Frías, to resign forced the legislature to acquiesce.
Regrettably, the 1874 treaty did not end the friction. Chile’s miners, who had long complained about the rough treatment they received at the hands of the Atacama police, continued to carp. And following the murder of their countryman Eliseo Arriagada, whom the local police had shot, the Chilean miners begged the Pinto government to protect them. Although this matter came to the attention of the Chilean Chamber of Deputies, the abuse did not cease, much to the dismay of many Chileans who still considered the Atacama to be theirs. What particularly galled some Chilean journalists was the fact that the Errázuriz government’s concessions to Bolivia had accomplished nothing: Bolivia continued to maltreat its Chilean workforce. In short, just as Christ died on the cross, “to redeem humanity,” wrote a Copiapó newspaper, “Chile in the name of American solidarity, had given its land to Bolivia.” Yet Chile still suffered from “offenses which daily wound its sons.” Thus in 1879, after years of not-so-silent suffering, Chile responded to Bolivia’s newly “elected” president Hilarión Daza’s latest insult—the unilateral imposition of higher export taxes—by seizing the land it had earlier ceded to Bolivia, thus causing the War of the Pacific, a contest that would soon involve Peru as well.
Casus foederis is derived from the Latin for "case of the alliance". In diplomatic terms, it describes a situation in which the terms of an alliance come into play, such as one nation being attacked by another.
Thus, in World War I, the treaties between Italy and Austria-Hungary, and Romania, which purported to require Italy and Romania to come to Austria’s aid if Austria was attacked by another nation, were not honored by either Italy or Romania because, as Winston Churchill wrote, “the casus fœderis had not arisen” because the attacks on Austria had not been “unprovoked.”
Also the Turco-German alliance involving the Ottoman Empire and German Reich in WWI worked on this basis, as the Ottomans attacked Russian Black Sea ports on 28 October, 1914.