This success led to a joint effort between Argentina, Brazil and Chile to negotiate a peaceful resolution to the United States' occupation of Veracruz, Mexico in April 1914. That May, the three nations' foreign ministers hosted U.S. officials in Canada, a conference instrumental in the withdrawal of U.S. troops that November. This also resulted in the 1915 ABC pact signed between the three and, like Brazil and Chile, Argentina thereafter pursued a pragmatic foreign policy, focused on preserving favorable trade relationships. This policy was in evidence during the 1933 Roca-Runciman Treaty, which secured Argentine markets among British colonies, and in the Argentine position during the Chaco War. Resulting from the 1928 discovery of petroleum in the area, the dispute developed into war after Bolivia's appeal for Argentine intervention in what it saw as Paraguayan incursions into potentially oil-rich lands were rejected. Bolivia invaded in July 1932 and, despite its legitimate claim to what historically had been its territory, its government's ties to Standard Oil of New Jersey (with whom the Argentine government was in dispute over its alleged pirating of oil in Salta Province) led Buenos Aires to withhold diplomatic efforts until, in June 1935, a cease-fire was signed. The laborious negotiations called in Buenos Aires by Argentine Foreign Minister Carlos Saavedra Lamas yielded him Latin America's first Nobel Prize for Peace in 1936 and a formal peace treaty in July 1938.