Tensions between the neighboring states had been rising for years, particularly over concerns about immigration and land reform. Geographically, Honduras is five times larger than El Salvador, but at the time, El Salvador's population was twice as large as that of Honduras. The combination led to the immigration of over 300,000 Salvadorans into Honduras by 1969. In 1962, in response to economic and political pressure, Honduras began a program of land reform that, by 1967, had resulted in expulsion of thousands of Salvadoran immigrants from Honduras and redistributing their land to Honduran citizens.
Thus, when the two nations met during qualification for the 1970 World Cup, the matches were charged with political emotion. The first leg was played in Tegucigalpa on 8 June 1969, with the Honduran side claiming a 1-0 victory. On 15 June, El Salvador won the second leg 3-0 in the city of San Salvador. Riots broke out before and after the match, resulting in the deaths of at least three Salvadorans. On 26 June, the teams participated in a playoff match played in Mexico City. El Salvador won 3-2 (a.e.t.), advancing to the Final Round of CONCACAF qualification, where they defeated Haiti to earn their first World Cup apperance.
On 26 June, El Salvador severed diplomatic ties with Honduras, citing the latter's failure to punish the alleged crimes or offer any reparations to El Salvador, and, the following day, Honduras severed its ties with El Salvador.
On 14 July, after a series of small border clashes, El Salvador launched a joint air and ground assault on Honduras. The Salvadoran forces advanced 8 km into Honduras before being bogged down with fuel and ammunition shortages. The Organization of American States intervened and brokered a cease-fire on 18 July, though El Salvador did not withdraw its troops until 2 August.
As a result of the conflict, between 60,000 and 130,000 Salvadorans had been expelled or fled from Honduras, while approximately 2,000 people were killed, the majority of whom were Honduran civilians.